imports Indicator_Function Countable_Set FuncSet Linear_Algebra Norm_Arith

(* title: HOL/Library/Topology_Euclidian_Space.thy Author: Amine Chaieb, University of Cambridge Author: Robert Himmelmann, TU Muenchen Author: Brian Huffman, Portland State University *) section ‹Elementary topology in Euclidean space.› theory Topology_Euclidean_Space imports "~~/src/HOL/Library/Indicator_Function" "~~/src/HOL/Library/Countable_Set" "~~/src/HOL/Library/FuncSet" Linear_Algebra Norm_Arith begin lemma image_affinity_interval: fixes c :: "'a::ordered_real_vector" shows "((λx. m *⇩_{R}x + c) ` {a..b}) = (if {a..b}={} then {} else if 0 <= m then {m *⇩_{R}a + c .. m *⇩_{R}b + c} else {m *⇩_{R}b + c .. m *⇩_{R}a + c})" apply (case_tac "m=0", force) apply (auto simp: scaleR_left_mono) apply (rule_tac x="inverse m *⇩_{R}(x-c)" in rev_image_eqI, auto simp: pos_le_divideR_eq le_diff_eq scaleR_left_mono_neg) apply (metis diff_le_eq inverse_inverse_eq order.not_eq_order_implies_strict pos_le_divideR_eq positive_imp_inverse_positive) apply (rule_tac x="inverse m *⇩_{R}(x-c)" in rev_image_eqI, auto simp: not_le neg_le_divideR_eq diff_le_eq) using le_diff_eq scaleR_le_cancel_left_neg apply fastforce done lemma dist_0_norm: fixes x :: "'a::real_normed_vector" shows "dist 0 x = norm x" unfolding dist_norm by simp lemma dist_double: "dist x y < d / 2 ⟹ dist x z < d / 2 ⟹ dist y z < d" using dist_triangle[of y z x] by (simp add: dist_commute) (* LEGACY *) lemma lim_subseq: "subseq r ⟹ s ⇢ l ⟹ (s ∘ r) ⇢ l" by (rule LIMSEQ_subseq_LIMSEQ) lemma countable_PiE: "finite I ⟹ (⋀i. i ∈ I ⟹ countable (F i)) ⟹ countable (PiE I F)" by (induct I arbitrary: F rule: finite_induct) (auto simp: PiE_insert_eq) lemma Lim_within_open: fixes f :: "'a::topological_space ⇒ 'b::topological_space" shows "a ∈ S ⟹ open S ⟹ (f ⤏ l)(at a within S) ⟷ (f ⤏ l)(at a)" by (fact tendsto_within_open) lemma Lim_within_open_NO_MATCH: fixes f :: "'a::topological_space ⇒ 'b::topological_space" shows "a ∈ S ⟹ NO_MATCH UNIV S ⟹ open S ⟹ (f ⤏ l)(at a within S) ⟷ (f ⤏ l)(at a)" using tendsto_within_open by blast lemma continuous_on_union: "closed s ⟹ closed t ⟹ continuous_on s f ⟹ continuous_on t f ⟹ continuous_on (s ∪ t) f" by (fact continuous_on_closed_Un) lemma continuous_on_cases: "closed s ⟹ closed t ⟹ continuous_on s f ⟹ continuous_on t g ⟹ ∀x. (x∈s ∧ ¬ P x) ∨ (x ∈ t ∧ P x) ⟶ f x = g x ⟹ continuous_on (s ∪ t) (λx. if P x then f x else g x)" by (rule continuous_on_If) auto subsection ‹Topological Basis› context topological_space begin definition "topological_basis B ⟷ (∀b∈B. open b) ∧ (∀x. open x ⟶ (∃B'. B' ⊆ B ∧ ⋃B' = x))" lemma topological_basis: "topological_basis B ⟷ (∀x. open x ⟷ (∃B'. B' ⊆ B ∧ ⋃B' = x))" unfolding topological_basis_def apply safe apply fastforce apply fastforce apply (erule_tac x="x" in allE) apply simp apply (rule_tac x="{x}" in exI) apply auto done lemma topological_basis_iff: assumes "⋀B'. B' ∈ B ⟹ open B'" shows "topological_basis B ⟷ (∀O'. open O' ⟶ (∀x∈O'. ∃B'∈B. x ∈ B' ∧ B' ⊆ O'))" (is "_ ⟷ ?rhs") proof safe fix O' and x::'a assume H: "topological_basis B" "open O'" "x ∈ O'" then have "(∃B'⊆B. ⋃B' = O')" by (simp add: topological_basis_def) then obtain B' where "B' ⊆ B" "O' = ⋃B'" by auto then show "∃B'∈B. x ∈ B' ∧ B' ⊆ O'" using H by auto next assume H: ?rhs show "topological_basis B" using assms unfolding topological_basis_def proof safe fix O' :: "'a set" assume "open O'" with H obtain f where "∀x∈O'. f x ∈ B ∧ x ∈ f x ∧ f x ⊆ O'" by (force intro: bchoice simp: Bex_def) then show "∃B'⊆B. ⋃B' = O'" by (auto intro: exI[where x="{f x |x. x ∈ O'}"]) qed qed lemma topological_basisI: assumes "⋀B'. B' ∈ B ⟹ open B'" and "⋀O' x. open O' ⟹ x ∈ O' ⟹ ∃B'∈B. x ∈ B' ∧ B' ⊆ O'" shows "topological_basis B" using assms by (subst topological_basis_iff) auto lemma topological_basisE: fixes O' assumes "topological_basis B" and "open O'" and "x ∈ O'" obtains B' where "B' ∈ B" "x ∈ B'" "B' ⊆ O'" proof atomize_elim from assms have "⋀B'. B'∈B ⟹ open B'" by (simp add: topological_basis_def) with topological_basis_iff assms show "∃B'. B' ∈ B ∧ x ∈ B' ∧ B' ⊆ O'" using assms by (simp add: Bex_def) qed lemma topological_basis_open: assumes "topological_basis B" and "X ∈ B" shows "open X" using assms by (simp add: topological_basis_def) lemma topological_basis_imp_subbasis: assumes B: "topological_basis B" shows "open = generate_topology B" proof (intro ext iffI) fix S :: "'a set" assume "open S" with B obtain B' where "B' ⊆ B" "S = ⋃B'" unfolding topological_basis_def by blast then show "generate_topology B S" by (auto intro: generate_topology.intros dest: topological_basis_open) next fix S :: "'a set" assume "generate_topology B S" then show "open S" by induct (auto dest: topological_basis_open[OF B]) qed lemma basis_dense: fixes B :: "'a set set" and f :: "'a set ⇒ 'a" assumes "topological_basis B" and choosefrom_basis: "⋀B'. B' ≠ {} ⟹ f B' ∈ B'" shows "∀X. open X ⟶ X ≠ {} ⟶ (∃B' ∈ B. f B' ∈ X)" proof (intro allI impI) fix X :: "'a set" assume "open X" and "X ≠ {}" from topological_basisE[OF ‹topological_basis B› ‹open X› choosefrom_basis[OF ‹X ≠ {}›]] obtain B' where "B' ∈ B" "f X ∈ B'" "B' ⊆ X" . then show "∃B'∈B. f B' ∈ X" by (auto intro!: choosefrom_basis) qed end lemma topological_basis_prod: assumes A: "topological_basis A" and B: "topological_basis B" shows "topological_basis ((λ(a, b). a × b) ` (A × B))" unfolding topological_basis_def proof (safe, simp_all del: ex_simps add: subset_image_iff ex_simps(1)[symmetric]) fix S :: "('a × 'b) set" assume "open S" then show "∃X⊆A × B. (⋃(a,b)∈X. a × b) = S" proof (safe intro!: exI[of _ "{x∈A × B. fst x × snd x ⊆ S}"]) fix x y assume "(x, y) ∈ S" from open_prod_elim[OF ‹open S› this] obtain a b where a: "open a""x ∈ a" and b: "open b" "y ∈ b" and "a × b ⊆ S" by (metis mem_Sigma_iff) moreover from A a obtain A0 where "A0 ∈ A" "x ∈ A0" "A0 ⊆ a" by (rule topological_basisE) moreover from B b obtain B0 where "B0 ∈ B" "y ∈ B0" "B0 ⊆ b" by (rule topological_basisE) ultimately show "(x, y) ∈ (⋃(a, b)∈{X ∈ A × B. fst X × snd X ⊆ S}. a × b)" by (intro UN_I[of "(A0, B0)"]) auto qed auto qed (metis A B topological_basis_open open_Times) subsection ‹Countable Basis› locale countable_basis = fixes B :: "'a::topological_space set set" assumes is_basis: "topological_basis B" and countable_basis: "countable B" begin lemma open_countable_basis_ex: assumes "open X" shows "∃B' ⊆ B. X = ⋃B'" using assms countable_basis is_basis unfolding topological_basis_def by blast lemma open_countable_basisE: assumes "open X" obtains B' where "B' ⊆ B" "X = ⋃B'" using assms open_countable_basis_ex by (atomize_elim) simp lemma countable_dense_exists: "∃D::'a set. countable D ∧ (∀X. open X ⟶ X ≠ {} ⟶ (∃d ∈ D. d ∈ X))" proof - let ?f = "(λB'. SOME x. x ∈ B')" have "countable (?f ` B)" using countable_basis by simp with basis_dense[OF is_basis, of ?f] show ?thesis by (intro exI[where x="?f ` B"]) (metis (mono_tags) all_not_in_conv imageI someI) qed lemma countable_dense_setE: obtains D :: "'a set" where "countable D" "⋀X. open X ⟹ X ≠ {} ⟹ ∃d ∈ D. d ∈ X" using countable_dense_exists by blast end lemma (in first_countable_topology) first_countable_basisE: obtains A where "countable A" "⋀a. a ∈ A ⟹ x ∈ a" "⋀a. a ∈ A ⟹ open a" "⋀S. open S ⟹ x ∈ S ⟹ (∃a∈A. a ⊆ S)" using first_countable_basis[of x] apply atomize_elim apply (elim exE) apply (rule_tac x="range A" in exI) apply auto done lemma (in first_countable_topology) first_countable_basis_Int_stableE: obtains A where "countable A" "⋀a. a ∈ A ⟹ x ∈ a" "⋀a. a ∈ A ⟹ open a" "⋀S. open S ⟹ x ∈ S ⟹ (∃a∈A. a ⊆ S)" "⋀a b. a ∈ A ⟹ b ∈ A ⟹ a ∩ b ∈ A" proof atomize_elim obtain A' where A': "countable A'" "⋀a. a ∈ A' ⟹ x ∈ a" "⋀a. a ∈ A' ⟹ open a" "⋀S. open S ⟹ x ∈ S ⟹ ∃a∈A'. a ⊆ S" by (rule first_countable_basisE) blast def A ≡ "(λN. ⋂((λn. from_nat_into A' n) ` N)) ` (Collect finite::nat set set)" then show "∃A. countable A ∧ (∀a. a ∈ A ⟶ x ∈ a) ∧ (∀a. a ∈ A ⟶ open a) ∧ (∀S. open S ⟶ x ∈ S ⟶ (∃a∈A. a ⊆ S)) ∧ (∀a b. a ∈ A ⟶ b ∈ A ⟶ a ∩ b ∈ A)" proof (safe intro!: exI[where x=A]) show "countable A" unfolding A_def by (intro countable_image countable_Collect_finite) fix a assume "a ∈ A" then show "x ∈ a" "open a" using A'(4)[OF open_UNIV] by (auto simp: A_def intro: A' from_nat_into) next let ?int = "λN. ⋂(from_nat_into A' ` N)" fix a b assume "a ∈ A" "b ∈ A" then obtain N M where "a = ?int N" "b = ?int M" "finite (N ∪ M)" by (auto simp: A_def) then show "a ∩ b ∈ A" by (auto simp: A_def intro!: image_eqI[where x="N ∪ M"]) next fix S assume "open S" "x ∈ S" then obtain a where a: "a∈A'" "a ⊆ S" using A' by blast then show "∃a∈A. a ⊆ S" using a A' by (intro bexI[where x=a]) (auto simp: A_def intro: image_eqI[where x="{to_nat_on A' a}"]) qed qed lemma (in topological_space) first_countableI: assumes "countable A" and 1: "⋀a. a ∈ A ⟹ x ∈ a" "⋀a. a ∈ A ⟹ open a" and 2: "⋀S. open S ⟹ x ∈ S ⟹ ∃a∈A. a ⊆ S" shows "∃A::nat ⇒ 'a set. (∀i. x ∈ A i ∧ open (A i)) ∧ (∀S. open S ∧ x ∈ S ⟶ (∃i. A i ⊆ S))" proof (safe intro!: exI[of _ "from_nat_into A"]) fix i have "A ≠ {}" using 2[of UNIV] by auto show "x ∈ from_nat_into A i" "open (from_nat_into A i)" using range_from_nat_into_subset[OF ‹A ≠ {}›] 1 by auto next fix S assume "open S" "x∈S" from 2[OF this] show "∃i. from_nat_into A i ⊆ S" using subset_range_from_nat_into[OF ‹countable A›] by auto qed instance prod :: (first_countable_topology, first_countable_topology) first_countable_topology proof fix x :: "'a × 'b" obtain A where A: "countable A" "⋀a. a ∈ A ⟹ fst x ∈ a" "⋀a. a ∈ A ⟹ open a" "⋀S. open S ⟹ fst x ∈ S ⟹ ∃a∈A. a ⊆ S" by (rule first_countable_basisE[of "fst x"]) blast obtain B where B: "countable B" "⋀a. a ∈ B ⟹ snd x ∈ a" "⋀a. a ∈ B ⟹ open a" "⋀S. open S ⟹ snd x ∈ S ⟹ ∃a∈B. a ⊆ S" by (rule first_countable_basisE[of "snd x"]) blast show "∃A::nat ⇒ ('a × 'b) set. (∀i. x ∈ A i ∧ open (A i)) ∧ (∀S. open S ∧ x ∈ S ⟶ (∃i. A i ⊆ S))" proof (rule first_countableI[of "(λ(a, b). a × b) ` (A × B)"], safe) fix a b assume x: "a ∈ A" "b ∈ B" with A(2, 3)[of a] B(2, 3)[of b] show "x ∈ a × b" and "open (a × b)" unfolding mem_Times_iff by (auto intro: open_Times) next fix S assume "open S" "x ∈ S" then obtain a' b' where a'b': "open a'" "open b'" "x ∈ a' × b'" "a' × b' ⊆ S" by (rule open_prod_elim) moreover from a'b' A(4)[of a'] B(4)[of b'] obtain a b where "a ∈ A" "a ⊆ a'" "b ∈ B" "b ⊆ b'" by auto ultimately show "∃a∈(λ(a, b). a × b) ` (A × B). a ⊆ S" by (auto intro!: bexI[of _ "a × b"] bexI[of _ a] bexI[of _ b]) qed (simp add: A B) qed class second_countable_topology = topological_space + assumes ex_countable_subbasis: "∃B::'a::topological_space set set. countable B ∧ open = generate_topology B" begin lemma ex_countable_basis: "∃B::'a set set. countable B ∧ topological_basis B" proof - from ex_countable_subbasis obtain B where B: "countable B" "open = generate_topology B" by blast let ?B = "Inter ` {b. finite b ∧ b ⊆ B }" show ?thesis proof (intro exI conjI) show "countable ?B" by (intro countable_image countable_Collect_finite_subset B) { fix S assume "open S" then have "∃B'⊆{b. finite b ∧ b ⊆ B}. (⋃b∈B'. ⋂b) = S" unfolding B proof induct case UNIV show ?case by (intro exI[of _ "{{}}"]) simp next case (Int a b) then obtain x y where x: "a = UNION x Inter" "⋀i. i ∈ x ⟹ finite i ∧ i ⊆ B" and y: "b = UNION y Inter" "⋀i. i ∈ y ⟹ finite i ∧ i ⊆ B" by blast show ?case unfolding x y Int_UN_distrib2 by (intro exI[of _ "{i ∪ j| i j. i ∈ x ∧ j ∈ y}"]) (auto dest: x(2) y(2)) next case (UN K) then have "∀k∈K. ∃B'⊆{b. finite b ∧ b ⊆ B}. UNION B' Inter = k" by auto then obtain k where "∀ka∈K. k ka ⊆ {b. finite b ∧ b ⊆ B} ∧ UNION (k ka) Inter = ka" unfolding bchoice_iff .. then show "∃B'⊆{b. finite b ∧ b ⊆ B}. UNION B' Inter = ⋃K" by (intro exI[of _ "UNION K k"]) auto next case (Basis S) then show ?case by (intro exI[of _ "{{S}}"]) auto qed then have "(∃B'⊆Inter ` {b. finite b ∧ b ⊆ B}. ⋃B' = S)" unfolding subset_image_iff by blast } then show "topological_basis ?B" unfolding topological_space_class.topological_basis_def by (safe intro!: topological_space_class.open_Inter) (simp_all add: B generate_topology.Basis subset_eq) qed qed end sublocale second_countable_topology < countable_basis "SOME B. countable B ∧ topological_basis B" using someI_ex[OF ex_countable_basis] by unfold_locales safe instance prod :: (second_countable_topology, second_countable_topology) second_countable_topology proof obtain A :: "'a set set" where "countable A" "topological_basis A" using ex_countable_basis by auto moreover obtain B :: "'b set set" where "countable B" "topological_basis B" using ex_countable_basis by auto ultimately show "∃B::('a × 'b) set set. countable B ∧ open = generate_topology B" by (auto intro!: exI[of _ "(λ(a, b). a × b) ` (A × B)"] topological_basis_prod topological_basis_imp_subbasis) qed instance second_countable_topology ⊆ first_countable_topology proof fix x :: 'a def B ≡ "SOME B::'a set set. countable B ∧ topological_basis B" then have B: "countable B" "topological_basis B" using countable_basis is_basis by (auto simp: countable_basis is_basis) then show "∃A::nat ⇒ 'a set. (∀i. x ∈ A i ∧ open (A i)) ∧ (∀S. open S ∧ x ∈ S ⟶ (∃i. A i ⊆ S))" by (intro first_countableI[of "{b∈B. x ∈ b}"]) (fastforce simp: topological_space_class.topological_basis_def)+ qed subsection ‹Polish spaces› text ‹Textbooks define Polish spaces as completely metrizable. We assume the topology to be complete for a given metric.› class polish_space = complete_space + second_countable_topology subsection ‹General notion of a topology as a value› definition "istopology L ⟷ L {} ∧ (∀S T. L S ⟶ L T ⟶ L (S ∩ T)) ∧ (∀K. Ball K L ⟶ L (⋃K))" typedef 'a topology = "{L::('a set) ⇒ bool. istopology L}" morphisms "openin" "topology" unfolding istopology_def by blast lemma istopology_open_in[intro]: "istopology(openin U)" using openin[of U] by blast lemma topology_inverse': "istopology U ⟹ openin (topology U) = U" using topology_inverse[unfolded mem_Collect_eq] . lemma topology_inverse_iff: "istopology U ⟷ openin (topology U) = U" using topology_inverse[of U] istopology_open_in[of "topology U"] by auto lemma topology_eq: "T1 = T2 ⟷ (∀S. openin T1 S ⟷ openin T2 S)" proof assume "T1 = T2" then show "∀S. openin T1 S ⟷ openin T2 S" by simp next assume H: "∀S. openin T1 S ⟷ openin T2 S" then have "openin T1 = openin T2" by (simp add: fun_eq_iff) then have "topology (openin T1) = topology (openin T2)" by simp then show "T1 = T2" unfolding openin_inverse . qed text‹Infer the "universe" from union of all sets in the topology.› definition "topspace T = ⋃{S. openin T S}" subsubsection ‹Main properties of open sets› lemma openin_clauses: fixes U :: "'a topology" shows "openin U {}" "⋀S T. openin U S ⟹ openin U T ⟹ openin U (S∩T)" "⋀K. (∀S ∈ K. openin U S) ⟹ openin U (⋃K)" using openin[of U] unfolding istopology_def mem_Collect_eq by fast+ lemma openin_subset[intro]: "openin U S ⟹ S ⊆ topspace U" unfolding topspace_def by blast lemma openin_empty[simp]: "openin U {}" by (simp add: openin_clauses) lemma openin_Int[intro]: "openin U S ⟹ openin U T ⟹ openin U (S ∩ T)" using openin_clauses by simp lemma openin_Union[intro]: "(∀S ∈K. openin U S) ⟹ openin U (⋃K)" using openin_clauses by simp lemma openin_Un[intro]: "openin U S ⟹ openin U T ⟹ openin U (S ∪ T)" using openin_Union[of "{S,T}" U] by auto lemma openin_topspace[intro, simp]: "openin U (topspace U)" by (simp add: openin_Union topspace_def) lemma openin_subopen: "openin U S ⟷ (∀x ∈ S. ∃T. openin U T ∧ x ∈ T ∧ T ⊆ S)" (is "?lhs ⟷ ?rhs") proof assume ?lhs then show ?rhs by auto next assume H: ?rhs let ?t = "⋃{T. openin U T ∧ T ⊆ S}" have "openin U ?t" by (simp add: openin_Union) also have "?t = S" using H by auto finally show "openin U S" . qed subsubsection ‹Closed sets› definition "closedin U S ⟷ S ⊆ topspace U ∧ openin U (topspace U - S)" lemma closedin_subset: "closedin U S ⟹ S ⊆ topspace U" by (metis closedin_def) lemma closedin_empty[simp]: "closedin U {}" by (simp add: closedin_def) lemma closedin_topspace[intro, simp]: "closedin U (topspace U)" by (simp add: closedin_def) lemma closedin_Un[intro]: "closedin U S ⟹ closedin U T ⟹ closedin U (S ∪ T)" by (auto simp add: Diff_Un closedin_def) lemma Diff_Inter[intro]: "A - ⋂S = ⋃{A - s|s. s∈S}" by auto lemma closedin_Inter[intro]: assumes Ke: "K ≠ {}" and Kc: "⋀S. S ∈K ⟹ closedin U S" shows "closedin U (⋂K)" using Ke Kc unfolding closedin_def Diff_Inter by auto lemma closedin_INT[intro]: assumes "A ≠ {}" "⋀x. x ∈ A ⟹ closedin U (B x)" shows "closedin U (⋂x∈A. B x)" unfolding Inter_image_eq [symmetric] apply (rule closedin_Inter) using assms apply auto done lemma closedin_Int[intro]: "closedin U S ⟹ closedin U T ⟹ closedin U (S ∩ T)" using closedin_Inter[of "{S,T}" U] by auto lemma openin_closedin_eq: "openin U S ⟷ S ⊆ topspace U ∧ closedin U (topspace U - S)" apply (auto simp add: closedin_def Diff_Diff_Int inf_absorb2) apply (metis openin_subset subset_eq) done lemma openin_closedin: "S ⊆ topspace U ⟹ (openin U S ⟷ closedin U (topspace U - S))" by (simp add: openin_closedin_eq) lemma openin_diff[intro]: assumes oS: "openin U S" and cT: "closedin U T" shows "openin U (S - T)" proof - have "S - T = S ∩ (topspace U - T)" using openin_subset[of U S] oS cT by (auto simp add: topspace_def openin_subset) then show ?thesis using oS cT by (auto simp add: closedin_def) qed lemma closedin_diff[intro]: assumes oS: "closedin U S" and cT: "openin U T" shows "closedin U (S - T)" proof - have "S - T = S ∩ (topspace U - T)" using closedin_subset[of U S] oS cT by (auto simp add: topspace_def) then show ?thesis using oS cT by (auto simp add: openin_closedin_eq) qed subsubsection ‹Subspace topology› definition "subtopology U V = topology (λT. ∃S. T = S ∩ V ∧ openin U S)" lemma istopology_subtopology: "istopology (λT. ∃S. T = S ∩ V ∧ openin U S)" (is "istopology ?L") proof - have "?L {}" by blast { fix A B assume A: "?L A" and B: "?L B" from A B obtain Sa and Sb where Sa: "openin U Sa" "A = Sa ∩ V" and Sb: "openin U Sb" "B = Sb ∩ V" by blast have "A ∩ B = (Sa ∩ Sb) ∩ V" "openin U (Sa ∩ Sb)" using Sa Sb by blast+ then have "?L (A ∩ B)" by blast } moreover { fix K assume K: "K ⊆ Collect ?L" have th0: "Collect ?L = (λS. S ∩ V) ` Collect (openin U)" by blast from K[unfolded th0 subset_image_iff] obtain Sk where Sk: "Sk ⊆ Collect (openin U)" "K = (λS. S ∩ V) ` Sk" by blast have "⋃K = (⋃Sk) ∩ V" using Sk by auto moreover have "openin U (⋃Sk)" using Sk by (auto simp add: subset_eq) ultimately have "?L (⋃K)" by blast } ultimately show ?thesis unfolding subset_eq mem_Collect_eq istopology_def by blast qed lemma openin_subtopology: "openin (subtopology U V) S ⟷ (∃T. openin U T ∧ S = T ∩ V)" unfolding subtopology_def topology_inverse'[OF istopology_subtopology] by auto lemma topspace_subtopology: "topspace (subtopology U V) = topspace U ∩ V" by (auto simp add: topspace_def openin_subtopology) lemma closedin_subtopology: "closedin (subtopology U V) S ⟷ (∃T. closedin U T ∧ S = T ∩ V)" unfolding closedin_def topspace_subtopology by (auto simp add: openin_subtopology) lemma openin_subtopology_refl: "openin (subtopology U V) V ⟷ V ⊆ topspace U" unfolding openin_subtopology by auto (metis IntD1 in_mono openin_subset) lemma subtopology_superset: assumes UV: "topspace U ⊆ V" shows "subtopology U V = U" proof - { fix S { fix T assume T: "openin U T" "S = T ∩ V" from T openin_subset[OF T(1)] UV have eq: "S = T" by blast have "openin U S" unfolding eq using T by blast } moreover { assume S: "openin U S" then have "∃T. openin U T ∧ S = T ∩ V" using openin_subset[OF S] UV by auto } ultimately have "(∃T. openin U T ∧ S = T ∩ V) ⟷ openin U S" by blast } then show ?thesis unfolding topology_eq openin_subtopology by blast qed lemma subtopology_topspace[simp]: "subtopology U (topspace U) = U" by (simp add: subtopology_superset) lemma subtopology_UNIV[simp]: "subtopology U UNIV = U" by (simp add: subtopology_superset) subsubsection ‹The standard Euclidean topology› definition euclidean :: "'a::topological_space topology" where "euclidean = topology open" lemma open_openin: "open S ⟷ openin euclidean S" unfolding euclidean_def apply (rule cong[where x=S and y=S]) apply (rule topology_inverse[symmetric]) apply (auto simp add: istopology_def) done lemma topspace_euclidean: "topspace euclidean = UNIV" apply (simp add: topspace_def) apply (rule set_eqI) apply (auto simp add: open_openin[symmetric]) done lemma topspace_euclidean_subtopology[simp]: "topspace (subtopology euclidean S) = S" by (simp add: topspace_euclidean topspace_subtopology) lemma closed_closedin: "closed S ⟷ closedin euclidean S" by (simp add: closed_def closedin_def topspace_euclidean open_openin Compl_eq_Diff_UNIV) lemma open_subopen: "open S ⟷ (∀x∈S. ∃T. open T ∧ x ∈ T ∧ T ⊆ S)" by (simp add: open_openin openin_subopen[symmetric]) text ‹Basic "localization" results are handy for connectedness.› lemma openin_open: "openin (subtopology euclidean U) S ⟷ (∃T. open T ∧ (S = U ∩ T))" by (auto simp add: openin_subtopology open_openin[symmetric]) lemma openin_open_Int[intro]: "open S ⟹ openin (subtopology euclidean U) (U ∩ S)" by (auto simp add: openin_open) lemma open_openin_trans[trans]: "open S ⟹ open T ⟹ T ⊆ S ⟹ openin (subtopology euclidean S) T" by (metis Int_absorb1 openin_open_Int) lemma open_subset: "S ⊆ T ⟹ open S ⟹ openin (subtopology euclidean T) S" by (auto simp add: openin_open) lemma closedin_closed: "closedin (subtopology euclidean U) S ⟷ (∃T. closed T ∧ S = U ∩ T)" by (simp add: closedin_subtopology closed_closedin Int_ac) lemma closedin_closed_Int: "closed S ⟹ closedin (subtopology euclidean U) (U ∩ S)" by (metis closedin_closed) lemma closed_closedin_trans: "closed S ⟹ closed T ⟹ T ⊆ S ⟹ closedin (subtopology euclidean S) T" by (metis closedin_closed inf.absorb2) lemma closed_subset: "S ⊆ T ⟹ closed S ⟹ closedin (subtopology euclidean T) S" by (auto simp add: closedin_closed) lemma openin_euclidean_subtopology_iff: fixes S U :: "'a::metric_space set" shows "openin (subtopology euclidean U) S ⟷ S ⊆ U ∧ (∀x∈S. ∃e>0. ∀x'∈U. dist x' x < e ⟶ x'∈ S)" (is "?lhs ⟷ ?rhs") proof assume ?lhs then show ?rhs unfolding openin_open open_dist by blast next def T ≡ "{x. ∃a∈S. ∃d>0. (∀y∈U. dist y a < d ⟶ y ∈ S) ∧ dist x a < d}" have 1: "∀x∈T. ∃e>0. ∀y. dist y x < e ⟶ y ∈ T" unfolding T_def apply clarsimp apply (rule_tac x="d - dist x a" in exI) apply (clarsimp simp add: less_diff_eq) by (metis dist_commute dist_triangle_lt) assume ?rhs then have 2: "S = U ∩ T" unfolding T_def by auto (metis dist_self) from 1 2 show ?lhs unfolding openin_open open_dist by fast qed lemma connected_open_in: "connected s ⟷ ~(∃e1 e2. openin (subtopology euclidean s) e1 ∧ openin (subtopology euclidean s) e2 ∧ s ⊆ e1 ∪ e2 ∧ e1 ∩ e2 = {} ∧ e1 ≠ {} ∧ e2 ≠ {})" apply (simp add: connected_def openin_open, safe) apply (simp_all, blast+) ―‹slow› done lemma connected_open_in_eq: "connected s ⟷ ~(∃e1 e2. openin (subtopology euclidean s) e1 ∧ openin (subtopology euclidean s) e2 ∧ e1 ∪ e2 = s ∧ e1 ∩ e2 = {} ∧ e1 ≠ {} ∧ e2 ≠ {})" apply (simp add: connected_open_in, safe) apply blast by (metis Int_lower1 Un_subset_iff openin_open subset_antisym) lemma connected_closed_in: "connected s ⟷ ~(∃e1 e2. closedin (subtopology euclidean s) e1 ∧ closedin (subtopology euclidean s) e2 ∧ s ⊆ e1 ∪ e2 ∧ e1 ∩ e2 = {} ∧ e1 ≠ {} ∧ e2 ≠ {})" proof - { fix A B x x' assume s_sub: "s ⊆ A ∪ B" and disj: "A ∩ B ∩ s = {}" and x: "x ∈ s" "x ∈ B" and x': "x' ∈ s" "x' ∈ A" and cl: "closed A" "closed B" assume "∀e1. (∀T. closed T ⟶ e1 ≠ s ∩ T) ∨ (∀e2. e1 ∩ e2 = {} ⟶ s ⊆ e1 ∪ e2 ⟶ (∀T. closed T ⟶ e2 ≠ s ∩ T) ∨ e1 = {} ∨ e2 = {})" then have "⋀C D. s ∩ C = {} ∨ s ∩ D = {} ∨ s ∩ (C ∩ (s ∩ D)) ≠ {} ∨ ¬ s ⊆ s ∩ (C ∪ D) ∨ ¬ closed C ∨ ¬ closed D" by (metis (no_types) Int_Un_distrib Int_assoc) moreover have "s ∩ (A ∩ B) = {}" "s ∩ (A ∪ B) = s" "s ∩ B ≠ {}" using disj s_sub x by blast+ ultimately have "s ∩ A = {}" using cl by (metis inf.left_commute inf_bot_right order_refl) then have False using x' by blast } note * = this show ?thesis apply (simp add: connected_closed closedin_closed) apply (safe; simp) apply blast apply (blast intro: *) done qed lemma connected_closed_in_eq: "connected s ⟷ ~(∃e1 e2. closedin (subtopology euclidean s) e1 ∧ closedin (subtopology euclidean s) e2 ∧ e1 ∪ e2 = s ∧ e1 ∩ e2 = {} ∧ e1 ≠ {} ∧ e2 ≠ {})" apply (simp add: connected_closed_in, safe) apply blast by (metis Int_lower1 Un_subset_iff closedin_closed subset_antisym) text ‹These "transitivity" results are handy too› lemma openin_trans[trans]: "openin (subtopology euclidean T) S ⟹ openin (subtopology euclidean U) T ⟹ openin (subtopology euclidean U) S" unfolding open_openin openin_open by blast lemma openin_open_trans: "openin (subtopology euclidean T) S ⟹ open T ⟹ open S" by (auto simp add: openin_open intro: openin_trans) lemma closedin_trans[trans]: "closedin (subtopology euclidean T) S ⟹ closedin (subtopology euclidean U) T ⟹ closedin (subtopology euclidean U) S" by (auto simp add: closedin_closed closed_closedin closed_Inter Int_assoc) lemma closedin_closed_trans: "closedin (subtopology euclidean T) S ⟹ closed T ⟹ closed S" by (auto simp add: closedin_closed intro: closedin_trans) lemma openin_subtopology_inter_subset: "openin (subtopology euclidean u) (u ∩ s) ∧ v ⊆ u ⟹ openin (subtopology euclidean v) (v ∩ s)" by (auto simp: openin_subtopology) lemma openin_open_eq: "open s ⟹ (openin (subtopology euclidean s) t ⟷ open t ∧ t ⊆ s)" using open_subset openin_open_trans openin_subset by fastforce subsection ‹Open and closed balls› definition ball :: "'a::metric_space ⇒ real ⇒ 'a set" where "ball x e = {y. dist x y < e}" definition cball :: "'a::metric_space ⇒ real ⇒ 'a set" where "cball x e = {y. dist x y ≤ e}" definition sphere :: "'a::metric_space ⇒ real ⇒ 'a set" where "sphere x e = {y. dist x y = e}" lemma mem_ball [simp]: "y ∈ ball x e ⟷ dist x y < e" by (simp add: ball_def) lemma mem_cball [simp]: "y ∈ cball x e ⟷ dist x y ≤ e" by (simp add: cball_def) lemma mem_sphere [simp]: "y ∈ sphere x e ⟷ dist x y = e" by (simp add: sphere_def) lemma ball_trivial [simp]: "ball x 0 = {}" by (simp add: ball_def) lemma cball_trivial [simp]: "cball x 0 = {x}" by (simp add: cball_def) lemma mem_ball_0 [simp]: fixes x :: "'a::real_normed_vector" shows "x ∈ ball 0 e ⟷ norm x < e" by (simp add: dist_norm) lemma mem_cball_0 [simp]: fixes x :: "'a::real_normed_vector" shows "x ∈ cball 0 e ⟷ norm x ≤ e" by (simp add: dist_norm) lemma centre_in_ball [simp]: "x ∈ ball x e ⟷ 0 < e" by simp lemma centre_in_cball [simp]: "x ∈ cball x e ⟷ 0 ≤ e" by simp lemma ball_subset_cball [simp,intro]: "ball x e ⊆ cball x e" by (simp add: subset_eq) lemma sphere_cball [simp,intro]: "sphere z r ⊆ cball z r" by force lemma subset_ball[intro]: "d ≤ e ⟹ ball x d ⊆ ball x e" by (simp add: subset_eq) lemma subset_cball[intro]: "d ≤ e ⟹ cball x d ⊆ cball x e" by (simp add: subset_eq) lemma ball_max_Un: "ball a (max r s) = ball a r ∪ ball a s" by (simp add: set_eq_iff) arith lemma ball_min_Int: "ball a (min r s) = ball a r ∩ ball a s" by (simp add: set_eq_iff) lemma cball_diff_eq_sphere: "cball a r - ball a r = {x. dist x a = r}" by (auto simp: cball_def ball_def dist_commute) lemma open_ball [intro, simp]: "open (ball x e)" proof - have "open (dist x -` {..<e})" by (intro open_vimage open_lessThan continuous_intros) also have "dist x -` {..<e} = ball x e" by auto finally show ?thesis . qed lemma open_contains_ball: "open S ⟷ (∀x∈S. ∃e>0. ball x e ⊆ S)" unfolding open_dist subset_eq mem_ball Ball_def dist_commute .. lemma openE[elim?]: assumes "open S" "x∈S" obtains e where "e>0" "ball x e ⊆ S" using assms unfolding open_contains_ball by auto lemma open_contains_ball_eq: "open S ⟹ ∀x. x∈S ⟷ (∃e>0. ball x e ⊆ S)" by (metis open_contains_ball subset_eq centre_in_ball) lemma ball_eq_empty[simp]: "ball x e = {} ⟷ e ≤ 0" unfolding mem_ball set_eq_iff apply (simp add: not_less) apply (metis zero_le_dist order_trans dist_self) done lemma ball_empty: "e ≤ 0 ⟹ ball x e = {}" by simp lemma euclidean_dist_l2: fixes x y :: "'a :: euclidean_space" shows "dist x y = setL2 (λi. dist (x ∙ i) (y ∙ i)) Basis" unfolding dist_norm norm_eq_sqrt_inner setL2_def by (subst euclidean_inner) (simp add: power2_eq_square inner_diff_left) lemma eventually_nhds_ball: "d > 0 ⟹ eventually (λx. x ∈ ball z d) (nhds z)" by (rule eventually_nhds_in_open) simp_all lemma eventually_at_ball: "d > 0 ⟹ eventually (λt. t ∈ ball z d ∧ t ∈ A) (at z within A)" unfolding eventually_at by (intro exI[of _ d]) (simp_all add: dist_commute) lemma eventually_at_ball': "d > 0 ⟹ eventually (λt. t ∈ ball z d ∧ t ≠ z ∧ t ∈ A) (at z within A)" unfolding eventually_at by (intro exI[of _ d]) (simp_all add: dist_commute) subsection ‹Boxes› abbreviation One :: "'a::euclidean_space" where "One ≡ ∑Basis" definition (in euclidean_space) eucl_less (infix "<e" 50) where "eucl_less a b ⟷ (∀i∈Basis. a ∙ i < b ∙ i)" definition box_eucl_less: "box a b = {x. a <e x ∧ x <e b}" definition "cbox a b = {x. ∀i∈Basis. a ∙ i ≤ x ∙ i ∧ x ∙ i ≤ b ∙ i}" lemma box_def: "box a b = {x. ∀i∈Basis. a ∙ i < x ∙ i ∧ x ∙ i < b ∙ i}" and in_box_eucl_less: "x ∈ box a b ⟷ a <e x ∧ x <e b" and mem_box: "x ∈ box a b ⟷ (∀i∈Basis. a ∙ i < x ∙ i ∧ x ∙ i < b ∙ i)" "x ∈ cbox a b ⟷ (∀i∈Basis. a ∙ i ≤ x ∙ i ∧ x ∙ i ≤ b ∙ i)" by (auto simp: box_eucl_less eucl_less_def cbox_def) lemma cbox_Pair_eq: "cbox (a, c) (b, d) = cbox a b × cbox c d" by (force simp: cbox_def Basis_prod_def) lemma cbox_Pair_iff [iff]: "(x, y) ∈ cbox (a, c) (b, d) ⟷ x ∈ cbox a b ∧ y ∈ cbox c d" by (force simp: cbox_Pair_eq) lemma cbox_Pair_eq_0: "cbox (a, c) (b, d) = {} ⟷ cbox a b = {} ∨ cbox c d = {}" by (force simp: cbox_Pair_eq) lemma swap_cbox_Pair [simp]: "prod.swap ` cbox (c, a) (d, b) = cbox (a,c) (b,d)" by auto lemma mem_box_real[simp]: "(x::real) ∈ box a b ⟷ a < x ∧ x < b" "(x::real) ∈ cbox a b ⟷ a ≤ x ∧ x ≤ b" by (auto simp: mem_box) lemma box_real[simp]: fixes a b:: real shows "box a b = {a <..< b}" "cbox a b = {a .. b}" by auto lemma box_Int_box: fixes a :: "'a::euclidean_space" shows "box a b ∩ box c d = box (∑i∈Basis. max (a∙i) (c∙i) *⇩_{R}i) (∑i∈Basis. min (b∙i) (d∙i) *⇩_{R}i)" unfolding set_eq_iff and Int_iff and mem_box by auto lemma rational_boxes: fixes x :: "'a::euclidean_space" assumes "e > 0" shows "∃a b. (∀i∈Basis. a ∙ i ∈ ℚ ∧ b ∙ i ∈ ℚ ) ∧ x ∈ box a b ∧ box a b ⊆ ball x e" proof - def e' ≡ "e / (2 * sqrt (real (DIM ('a))))" then have e: "e' > 0" using assms by (auto simp: DIM_positive) have "∀i. ∃y. y ∈ ℚ ∧ y < x ∙ i ∧ x ∙ i - y < e'" (is "∀i. ?th i") proof fix i from Rats_dense_in_real[of "x ∙ i - e'" "x ∙ i"] e show "?th i" by auto qed from choice[OF this] obtain a where a: "∀xa. a xa ∈ ℚ ∧ a xa < x ∙ xa ∧ x ∙ xa - a xa < e'" .. have "∀i. ∃y. y ∈ ℚ ∧ x ∙ i < y ∧ y - x ∙ i < e'" (is "∀i. ?th i") proof fix i from Rats_dense_in_real[of "x ∙ i" "x ∙ i + e'"] e show "?th i" by auto qed from choice[OF this] obtain b where b: "∀xa. b xa ∈ ℚ ∧ x ∙ xa < b xa ∧ b xa - x ∙ xa < e'" .. let ?a = "∑i∈Basis. a i *⇩_{R}i" and ?b = "∑i∈Basis. b i *⇩_{R}i" show ?thesis proof (rule exI[of _ ?a], rule exI[of _ ?b], safe) fix y :: 'a assume *: "y ∈ box ?a ?b" have "dist x y = sqrt (∑i∈Basis. (dist (x ∙ i) (y ∙ i))⇧^{2})" unfolding setL2_def[symmetric] by (rule euclidean_dist_l2) also have "… < sqrt (∑(i::'a)∈Basis. e^2 / real (DIM('a)))" proof (rule real_sqrt_less_mono, rule setsum_strict_mono) fix i :: "'a" assume i: "i ∈ Basis" have "a i < y∙i ∧ y∙i < b i" using * i by (auto simp: box_def) moreover have "a i < x∙i" "x∙i - a i < e'" using a by auto moreover have "x∙i < b i" "b i - x∙i < e'" using b by auto ultimately have "¦x∙i - y∙i¦ < 2 * e'" by auto then have "dist (x ∙ i) (y ∙ i) < e/sqrt (real (DIM('a)))" unfolding e'_def by (auto simp: dist_real_def) then have "(dist (x ∙ i) (y ∙ i))⇧^{2}< (e/sqrt (real (DIM('a))))⇧^{2}" by (rule power_strict_mono) auto then show "(dist (x ∙ i) (y ∙ i))⇧^{2}< e⇧^{2}/ real DIM('a)" by (simp add: power_divide) qed auto also have "… = e" using ‹0 < e› by simp finally show "y ∈ ball x e" by (auto simp: ball_def) qed (insert a b, auto simp: box_def) qed lemma open_UNION_box: fixes M :: "'a::euclidean_space set" assumes "open M" defines "a' ≡ λf :: 'a ⇒ real × real. (∑(i::'a)∈Basis. fst (f i) *⇩_{R}i)" defines "b' ≡ λf :: 'a ⇒ real × real. (∑(i::'a)∈Basis. snd (f i) *⇩_{R}i)" defines "I ≡ {f∈Basis →⇩_{E}ℚ × ℚ. box (a' f) (b' f) ⊆ M}" shows "M = (⋃f∈I. box (a' f) (b' f))" proof - have "x ∈ (⋃f∈I. box (a' f) (b' f))" if "x ∈ M" for x proof - obtain e where e: "e > 0" "ball x e ⊆ M" using openE[OF ‹open M› ‹x ∈ M›] by auto moreover obtain a b where ab: "x ∈ box a b" "∀i ∈ Basis. a ∙ i ∈ ℚ" "∀i∈Basis. b ∙ i ∈ ℚ" "box a b ⊆ ball x e" using rational_boxes[OF e(1)] by metis ultimately show ?thesis by (intro UN_I[of "λi∈Basis. (a ∙ i, b ∙ i)"]) (auto simp: euclidean_representation I_def a'_def b'_def) qed then show ?thesis by (auto simp: I_def) qed lemma box_eq_empty: fixes a :: "'a::euclidean_space" shows "(box a b = {} ⟷ (∃i∈Basis. b∙i ≤ a∙i))" (is ?th1) and "(cbox a b = {} ⟷ (∃i∈Basis. b∙i < a∙i))" (is ?th2) proof - { fix i x assume i: "i∈Basis" and as:"b∙i ≤ a∙i" and x:"x∈box a b" then have "a ∙ i < x ∙ i ∧ x ∙ i < b ∙ i" unfolding mem_box by (auto simp: box_def) then have "a∙i < b∙i" by auto then have False using as by auto } moreover { assume as: "∀i∈Basis. ¬ (b∙i ≤ a∙i)" let ?x = "(1/2) *⇩_{R}(a + b)" { fix i :: 'a assume i: "i ∈ Basis" have "a∙i < b∙i" using as[THEN bspec[where x=i]] i by auto then have "a∙i < ((1/2) *⇩_{R}(a+b)) ∙ i" "((1/2) *⇩_{R}(a+b)) ∙ i < b∙i" by (auto simp: inner_add_left) } then have "box a b ≠ {}" using mem_box(1)[of "?x" a b] by auto } ultimately show ?th1 by blast { fix i x assume i: "i ∈ Basis" and as:"b∙i < a∙i" and x:"x∈cbox a b" then have "a ∙ i ≤ x ∙ i ∧ x ∙ i ≤ b ∙ i" unfolding mem_box by auto then have "a∙i ≤ b∙i" by auto then have False using as by auto } moreover { assume as:"∀i∈Basis. ¬ (b∙i < a∙i)" let ?x = "(1/2) *⇩_{R}(a + b)" { fix i :: 'a assume i:"i ∈ Basis" have "a∙i ≤ b∙i" using as[THEN bspec[where x=i]] i by auto then have "a∙i ≤ ((1/2) *⇩_{R}(a+b)) ∙ i" "((1/2) *⇩_{R}(a+b)) ∙ i ≤ b∙i" by (auto simp: inner_add_left) } then have "cbox a b ≠ {}" using mem_box(2)[of "?x" a b] by auto } ultimately show ?th2 by blast qed lemma box_ne_empty: fixes a :: "'a::euclidean_space" shows "cbox a b ≠ {} ⟷ (∀i∈Basis. a∙i ≤ b∙i)" and "box a b ≠ {} ⟷ (∀i∈Basis. a∙i < b∙i)" unfolding box_eq_empty[of a b] by fastforce+ lemma fixes a :: "'a::euclidean_space" shows cbox_sing: "cbox a a = {a}" and box_sing: "box a a = {}" unfolding set_eq_iff mem_box eq_iff [symmetric] by (auto intro!: euclidean_eqI[where 'a='a]) (metis all_not_in_conv nonempty_Basis) lemma subset_box_imp: fixes a :: "'a::euclidean_space" shows "(∀i∈Basis. a∙i ≤ c∙i ∧ d∙i ≤ b∙i) ⟹ cbox c d ⊆ cbox a b" and "(∀i∈Basis. a∙i < c∙i ∧ d∙i < b∙i) ⟹ cbox c d ⊆ box a b" and "(∀i∈Basis. a∙i ≤ c∙i ∧ d∙i ≤ b∙i) ⟹ box c d ⊆ cbox a b" and "(∀i∈Basis. a∙i ≤ c∙i ∧ d∙i ≤ b∙i) ⟹ box c d ⊆ box a b" unfolding subset_eq[unfolded Ball_def] unfolding mem_box by (best intro: order_trans less_le_trans le_less_trans less_imp_le)+ lemma box_subset_cbox: fixes a :: "'a::euclidean_space" shows "box a b ⊆ cbox a b" unfolding subset_eq [unfolded Ball_def] mem_box by (fast intro: less_imp_le) lemma subset_box: fixes a :: "'a::euclidean_space" shows "cbox c d ⊆ cbox a b ⟷ (∀i∈Basis. c∙i ≤ d∙i) --> (∀i∈Basis. a∙i ≤ c∙i ∧ d∙i ≤ b∙i)" (is ?th1) and "cbox c d ⊆ box a b ⟷ (∀i∈Basis. c∙i ≤ d∙i) --> (∀i∈Basis. a∙i < c∙i ∧ d∙i < b∙i)" (is ?th2) and "box c d ⊆ cbox a b ⟷ (∀i∈Basis. c∙i < d∙i) --> (∀i∈Basis. a∙i ≤ c∙i ∧ d∙i ≤ b∙i)" (is ?th3) and "box c d ⊆ box a b ⟷ (∀i∈Basis. c∙i < d∙i) --> (∀i∈Basis. a∙i ≤ c∙i ∧ d∙i ≤ b∙i)" (is ?th4) proof - show ?th1 unfolding subset_eq and Ball_def and mem_box by (auto intro: order_trans) show ?th2 unfolding subset_eq and Ball_def and mem_box by (auto intro: le_less_trans less_le_trans order_trans less_imp_le) { assume as: "box c d ⊆ cbox a b" "∀i∈Basis. c∙i < d∙i" then have "box c d ≠ {}" unfolding box_eq_empty by auto fix i :: 'a assume i: "i ∈ Basis" (** TODO combine the following two parts as done in the HOL_light version. **) { let ?x = "(∑j∈Basis. (if j=i then ((min (a∙j) (d∙j))+c∙j)/2 else (c∙j+d∙j)/2) *⇩_{R}j)::'a" assume as2: "a∙i > c∙i" { fix j :: 'a assume j: "j ∈ Basis" then have "c ∙ j < ?x ∙ j ∧ ?x ∙ j < d ∙ j" apply (cases "j = i") using as(2)[THEN bspec[where x=j]] i apply (auto simp add: as2) done } then have "?x∈box c d" using i unfolding mem_box by auto moreover have "?x ∉ cbox a b" unfolding mem_box apply auto apply (rule_tac x=i in bexI) using as(2)[THEN bspec[where x=i]] and as2 i apply auto done ultimately have False using as by auto } then have "a∙i ≤ c∙i" by (rule ccontr) auto moreover { let ?x = "(∑j∈Basis. (if j=i then ((max (b∙j) (c∙j))+d∙j)/2 else (c∙j+d∙j)/2) *⇩_{R}j)::'a" assume as2: "b∙i < d∙i" { fix j :: 'a assume "j∈Basis" then have "d ∙ j > ?x ∙ j ∧ ?x ∙ j > c ∙ j" apply (cases "j = i") using as(2)[THEN bspec[where x=j]] apply (auto simp add: as2) done } then have "?x∈box c d" unfolding mem_box by auto moreover have "?x∉cbox a b" unfolding mem_box apply auto apply (rule_tac x=i in bexI) using as(2)[THEN bspec[where x=i]] and as2 using i apply auto done ultimately have False using as by auto } then have "b∙i ≥ d∙i" by (rule ccontr) auto ultimately have "a∙i ≤ c∙i ∧ d∙i ≤ b∙i" by auto } note part1 = this show ?th3 unfolding subset_eq and Ball_def and mem_box apply (rule, rule, rule, rule) apply (rule part1) unfolding subset_eq and Ball_def and mem_box prefer 4 apply auto apply (erule_tac x=xa in allE, erule_tac x=xa in allE, fastforce)+ done { assume as: "box c d ⊆ box a b" "∀i∈Basis. c∙i < d∙i" fix i :: 'a assume i:"i∈Basis" from as(1) have "box c d ⊆ cbox a b" using box_subset_cbox[of a b] by auto then have "a∙i ≤ c∙i ∧ d∙i ≤ b∙i" using part1 and as(2) using i by auto } note * = this show ?th4 unfolding subset_eq and Ball_def and mem_box apply (rule, rule, rule, rule) apply (rule *) unfolding subset_eq and Ball_def and mem_box prefer 4 apply auto apply (erule_tac x=xa in allE, simp)+ done qed lemma inter_interval: fixes a :: "'a::euclidean_space" shows "cbox a b ∩ cbox c d = cbox (∑i∈Basis. max (a∙i) (c∙i) *⇩_{R}i) (∑i∈Basis. min (b∙i) (d∙i) *⇩_{R}i)" unfolding set_eq_iff and Int_iff and mem_box by auto lemma disjoint_interval: fixes a::"'a::euclidean_space" shows "cbox a b ∩ cbox c d = {} ⟷ (∃i∈Basis. (b∙i < a∙i ∨ d∙i < c∙i ∨ b∙i < c∙i ∨ d∙i < a∙i))" (is ?th1) and "cbox a b ∩ box c d = {} ⟷ (∃i∈Basis. (b∙i < a∙i ∨ d∙i ≤ c∙i ∨ b∙i ≤ c∙i ∨ d∙i ≤ a∙i))" (is ?th2) and "box a b ∩ cbox c d = {} ⟷ (∃i∈Basis. (b∙i ≤ a∙i ∨ d∙i < c∙i ∨ b∙i ≤ c∙i ∨ d∙i ≤ a∙i))" (is ?th3) and "box a b ∩ box c d = {} ⟷ (∃i∈Basis. (b∙i ≤ a∙i ∨ d∙i ≤ c∙i ∨ b∙i ≤ c∙i ∨ d∙i ≤ a∙i))" (is ?th4) proof - let ?z = "(∑i∈Basis. (((max (a∙i) (c∙i)) + (min (b∙i) (d∙i))) / 2) *⇩_{R}i)::'a" have **: "⋀P Q. (⋀i :: 'a. i ∈ Basis ⟹ Q ?z i ⟹ P i) ⟹ (⋀i x :: 'a. i ∈ Basis ⟹ P i ⟹ Q x i) ⟹ (∀x. ∃i∈Basis. Q x i) ⟷ (∃i∈Basis. P i)" by blast note * = set_eq_iff Int_iff empty_iff mem_box ball_conj_distrib[symmetric] eq_False ball_simps(10) show ?th1 unfolding * by (intro **) auto show ?th2 unfolding * by (intro **) auto show ?th3 unfolding * by (intro **) auto show ?th4 unfolding * by (intro **) auto qed lemma UN_box_eq_UNIV: "(⋃i::nat. box (- (real i *⇩_{R}One)) (real i *⇩_{R}One)) = UNIV" proof - have "¦x ∙ b¦ < real_of_int (⌈Max ((λb. ¦x ∙ b¦)`Basis)⌉ + 1)" if [simp]: "b ∈ Basis" for x b :: 'a proof - have "¦x ∙ b¦ ≤ real_of_int ⌈¦x ∙ b¦⌉" by (rule le_of_int_ceiling) also have "… ≤ real_of_int ⌈Max ((λb. ¦x ∙ b¦)`Basis)⌉" by (auto intro!: ceiling_mono) also have "… < real_of_int (⌈Max ((λb. ¦x ∙ b¦)`Basis)⌉ + 1)" by simp finally show ?thesis . qed then have "∃n::nat. ∀b∈Basis. ¦x ∙ b¦ < real n" for x :: 'a by (metis order.strict_trans reals_Archimedean2) moreover have "⋀x b::'a. ⋀n::nat. ¦x ∙ b¦ < real n ⟷ - real n < x ∙ b ∧ x ∙ b < real n" by auto ultimately show ?thesis by (auto simp: box_def inner_setsum_left inner_Basis setsum.If_cases) qed text ‹Intervals in general, including infinite and mixtures of open and closed.› definition "is_interval (s::('a::euclidean_space) set) ⟷ (∀a∈s. ∀b∈s. ∀x. (∀i∈Basis. ((a∙i ≤ x∙i ∧ x∙i ≤ b∙i) ∨ (b∙i ≤ x∙i ∧ x∙i ≤ a∙i))) ⟶ x ∈ s)" lemma is_interval_cbox: "is_interval (cbox a (b::'a::euclidean_space))" (is ?th1) and is_interval_box: "is_interval (box a b)" (is ?th2) unfolding is_interval_def mem_box Ball_def atLeastAtMost_iff by (meson order_trans le_less_trans less_le_trans less_trans)+ lemma is_interval_empty [iff]: "is_interval {}" unfolding is_interval_def by simp lemma is_interval_univ [iff]: "is_interval UNIV" unfolding is_interval_def by simp lemma mem_is_intervalI: assumes "is_interval s" assumes "a ∈ s" "b ∈ s" assumes "⋀i. i ∈ Basis ⟹ a ∙ i ≤ x ∙ i ∧ x ∙ i ≤ b ∙ i ∨ b ∙ i ≤ x ∙ i ∧ x ∙ i ≤ a ∙ i" shows "x ∈ s" by (rule assms(1)[simplified is_interval_def, rule_format, OF assms(2,3,4)]) lemma interval_subst: fixes S::"'a::euclidean_space set" assumes "is_interval S" assumes "x ∈ S" "y j ∈ S" assumes "j ∈ Basis" shows "(∑i∈Basis. (if i = j then y i ∙ i else x ∙ i) *⇩_{R}i) ∈ S" by (rule mem_is_intervalI[OF assms(1,2)]) (auto simp: assms) lemma mem_box_componentwiseI: fixes S::"'a::euclidean_space set" assumes "is_interval S" assumes "⋀i. i ∈ Basis ⟹ x ∙ i ∈ ((λx. x ∙ i) ` S)" shows "x ∈ S" proof - from assms have "∀i ∈ Basis. ∃s ∈ S. x ∙ i = s ∙ i" by auto with finite_Basis obtain s and bs::"'a list" where s: "⋀i. i ∈ Basis ⟹ x ∙ i = s i ∙ i" "⋀i. i ∈ Basis ⟹ s i ∈ S" and bs: "set bs = Basis" "distinct bs" by (metis finite_distinct_list) from nonempty_Basis s obtain j where j: "j ∈ Basis" "s j ∈ S" by blast def y ≡ "rec_list (s j) (λj _ Y. (∑i∈Basis. (if i = j then s i ∙ i else Y ∙ i) *⇩_{R}i))" have "x = (∑i∈Basis. (if i ∈ set bs then s i ∙ i else s j ∙ i) *⇩_{R}i)" using bs by (auto simp add: s(1)[symmetric] euclidean_representation) also have [symmetric]: "y bs = …" using bs(2) bs(1)[THEN equalityD1] by (induct bs) (auto simp: y_def euclidean_representation intro!: euclidean_eqI[where 'a='a]) also have "y bs ∈ S" using bs(1)[THEN equalityD1] apply (induct bs) apply (auto simp: y_def j) apply (rule interval_subst[OF assms(1)]) apply (auto simp: s) done finally show ?thesis . qed subsection‹Connectedness› lemma connected_local: "connected S ⟷ ¬ (∃e1 e2. openin (subtopology euclidean S) e1 ∧ openin (subtopology euclidean S) e2 ∧ S ⊆ e1 ∪ e2 ∧ e1 ∩ e2 = {} ∧ e1 ≠ {} ∧ e2 ≠ {})" unfolding connected_def openin_open by safe blast+ lemma exists_diff: fixes P :: "'a set ⇒ bool" shows "(∃S. P (- S)) ⟷ (∃S. P S)" (is "?lhs ⟷ ?rhs") proof - { assume "?lhs" then have ?rhs by blast } moreover { fix S assume H: "P S" have "S = - (- S)" by auto with H have "P (- (- S))" by metis } ultimately show ?thesis by metis qed lemma connected_clopen: "connected S ⟷ (∀T. openin (subtopology euclidean S) T ∧ closedin (subtopology euclidean S) T ⟶ T = {} ∨ T = S)" (is "?lhs ⟷ ?rhs") proof - have "¬ connected S ⟷ (∃e1 e2. open e1 ∧ open (- e2) ∧ S ⊆ e1 ∪ (- e2) ∧ e1 ∩ (- e2) ∩ S = {} ∧ e1 ∩ S ≠ {} ∧ (- e2) ∩ S ≠ {})" unfolding connected_def openin_open closedin_closed by (metis double_complement) then have th0: "connected S ⟷ ¬ (∃e2 e1. closed e2 ∧ open e1 ∧ S ⊆ e1 ∪ (- e2) ∧ e1 ∩ (- e2) ∩ S = {} ∧ e1 ∩ S ≠ {} ∧ (- e2) ∩ S ≠ {})" (is " _ ⟷ ¬ (∃e2 e1. ?P e2 e1)") apply (simp add: closed_def) apply metis done have th1: "?rhs ⟷ ¬ (∃t' t. closed t'∧t = S∩t' ∧ t≠{} ∧ t≠S ∧ (∃t'. open t' ∧ t = S ∩ t'))" (is "_ ⟷ ¬ (∃t' t. ?Q t' t)") unfolding connected_def openin_open closedin_closed by auto { fix e2 { fix e1 have "?P e2 e1 ⟷ (∃t. closed e2 ∧ t = S∩e2 ∧ open e1 ∧ t = S∩e1 ∧ t≠{} ∧ t ≠ S)" by auto } then have "(∃e1. ?P e2 e1) ⟷ (∃t. ?Q e2 t)" by metis } then have "∀e2. (∃e1. ?P e2 e1) ⟷ (∃t. ?Q e2 t)" by blast then show ?thesis unfolding th0 th1 by simp qed subsection‹Limit points› definition (in topological_space) islimpt:: "'a ⇒ 'a set ⇒ bool" (infixr "islimpt" 60) where "x islimpt S ⟷ (∀T. x∈T ⟶ open T ⟶ (∃y∈S. y∈T ∧ y≠x))" lemma islimptI: assumes "⋀T. x ∈ T ⟹ open T ⟹ ∃y∈S. y ∈ T ∧ y ≠ x" shows "x islimpt S" using assms unfolding islimpt_def by auto lemma islimptE: assumes "x islimpt S" and "x ∈ T" and "open T" obtains y where "y ∈ S" and "y ∈ T" and "y ≠ x" using assms unfolding islimpt_def by auto lemma islimpt_iff_eventually: "x islimpt S ⟷ ¬ eventually (λy. y ∉ S) (at x)" unfolding islimpt_def eventually_at_topological by auto lemma islimpt_subset: "x islimpt S ⟹ S ⊆ T ⟹ x islimpt T" unfolding islimpt_def by fast lemma islimpt_approachable: fixes x :: "'a::metric_space" shows "x islimpt S ⟷ (∀e>0. ∃x'∈S. x' ≠ x ∧ dist x' x < e)" unfolding islimpt_iff_eventually eventually_at by fast lemma islimpt_approachable_le: fixes x :: "'a::metric_space" shows "x islimpt S ⟷ (∀e>0. ∃x'∈ S. x' ≠ x ∧ dist x' x ≤ e)" unfolding islimpt_approachable using approachable_lt_le [where f="λy. dist y x" and P="λy. y ∉ S ∨ y = x", THEN arg_cong [where f=Not]] by (simp add: Bex_def conj_commute conj_left_commute) lemma islimpt_UNIV_iff: "x islimpt UNIV ⟷ ¬ open {x}" unfolding islimpt_def by (safe, fast, case_tac "T = {x}", fast, fast) lemma islimpt_punctured: "x islimpt S = x islimpt (S-{x})" unfolding islimpt_def by blast text ‹A perfect space has no isolated points.› lemma islimpt_UNIV [simp, intro]: "(x::'a::perfect_space) islimpt UNIV" unfolding islimpt_UNIV_iff by (rule not_open_singleton) lemma perfect_choose_dist: fixes x :: "'a::{perfect_space, metric_space}" shows "0 < r ⟹ ∃a. a ≠ x ∧ dist a x < r" using islimpt_UNIV [of x] by (simp add: islimpt_approachable) lemma closed_limpt: "closed S ⟷ (∀x. x islimpt S ⟶ x ∈ S)" unfolding closed_def apply (subst open_subopen) apply (simp add: islimpt_def subset_eq) apply (metis ComplE ComplI) done lemma islimpt_EMPTY[simp]: "¬ x islimpt {}" unfolding islimpt_def by auto lemma finite_set_avoid: fixes a :: "'a::metric_space" assumes fS: "finite S" shows "∃d>0. ∀x∈S. x ≠ a ⟶ d ≤ dist a x" proof (induct rule: finite_induct[OF fS]) case 1 then show ?case by (auto intro: zero_less_one) next case (2 x F) from 2 obtain d where d: "d > 0" "∀x∈F. x ≠ a ⟶ d ≤ dist a x" by blast show ?case proof (cases "x = a") case True then show ?thesis using d by auto next case False let ?d = "min d (dist a x)" have dp: "?d > 0" using False d(1) by auto from d have d': "∀x∈F. x ≠ a ⟶ ?d ≤ dist a x" by auto with dp False show ?thesis by (auto intro!: exI[where x="?d"]) qed qed lemma islimpt_Un: "x islimpt (S ∪ T) ⟷ x islimpt S ∨ x islimpt T" by (simp add: islimpt_iff_eventually eventually_conj_iff) lemma discrete_imp_closed: fixes S :: "'a::metric_space set" assumes e: "0 < e" and d: "∀x ∈ S. ∀y ∈ S. dist y x < e ⟶ y = x" shows "closed S" proof - { fix x assume C: "∀e>0. ∃x'∈S. x' ≠ x ∧ dist x' x < e" from e have e2: "e/2 > 0" by arith from C[rule_format, OF e2] obtain y where y: "y ∈ S" "y ≠ x" "dist y x < e/2" by blast let ?m = "min (e/2) (dist x y) " from e2 y(2) have mp: "?m > 0" by simp from C[rule_format, OF mp] obtain z where z: "z ∈ S" "z ≠ x" "dist z x < ?m" by blast have th: "dist z y < e" using z y by (intro dist_triangle_lt [where z=x], simp) from d[rule_format, OF y(1) z(1) th] y z have False by (auto simp add: dist_commute)} then show ?thesis by (metis islimpt_approachable closed_limpt [where 'a='a]) qed lemma closed_of_nat_image: "closed (of_nat ` A :: 'a :: real_normed_algebra_1 set)" by (rule discrete_imp_closed[of 1]) (auto simp: dist_of_nat) lemma closed_of_int_image: "closed (of_int ` A :: 'a :: real_normed_algebra_1 set)" by (rule discrete_imp_closed[of 1]) (auto simp: dist_of_int) lemma closed_Nats [simp]: "closed (ℕ :: 'a :: real_normed_algebra_1 set)" unfolding Nats_def by (rule closed_of_nat_image) lemma closed_Ints [simp]: "closed (ℤ :: 'a :: real_normed_algebra_1 set)" unfolding Ints_def by (rule closed_of_int_image) subsection ‹Interior of a Set› definition "interior S = ⋃{T. open T ∧ T ⊆ S}" lemma interiorI [intro?]: assumes "open T" and "x ∈ T" and "T ⊆ S" shows "x ∈ interior S" using assms unfolding interior_def by fast lemma interiorE [elim?]: assumes "x ∈ interior S" obtains T where "open T" and "x ∈ T" and "T ⊆ S" using assms unfolding interior_def by fast lemma open_interior [simp, intro]: "open (interior S)" by (simp add: interior_def open_Union) lemma interior_subset: "interior S ⊆ S" by (auto simp add: interior_def) lemma interior_maximal: "T ⊆ S ⟹ open T ⟹ T ⊆ interior S" by (auto simp add: interior_def) lemma interior_open: "open S ⟹ interior S = S" by (intro equalityI interior_subset interior_maximal subset_refl) lemma interior_eq: "interior S = S ⟷ open S" by (metis open_interior interior_open) lemma open_subset_interior: "open S ⟹ S ⊆ interior T ⟷ S ⊆ T" by (metis interior_maximal interior_subset subset_trans) lemma interior_empty [simp]: "interior {} = {}" using open_empty by (rule interior_open) lemma interior_UNIV [simp]: "interior UNIV = UNIV" using open_UNIV by (rule interior_open) lemma interior_interior [simp]: "interior (interior S) = interior S" using open_interior by (rule interior_open) lemma interior_mono: "S ⊆ T ⟹ interior S ⊆ interior T" by (auto simp add: interior_def) lemma interior_unique: assumes "T ⊆ S" and "open T" assumes "⋀T'. T' ⊆ S ⟹ open T' ⟹ T' ⊆ T" shows "interior S = T" by (intro equalityI assms interior_subset open_interior interior_maximal) lemma interior_singleton [simp]: fixes a :: "'a::perfect_space" shows "interior {a} = {}" apply (rule interior_unique, simp_all) using not_open_singleton subset_singletonD by fastforce lemma interior_Int [simp]: "interior (S ∩ T) = interior S ∩ interior T" by (intro equalityI Int_mono Int_greatest interior_mono Int_lower1 Int_lower2 interior_maximal interior_subset open_Int open_interior) lemma mem_interior: "x ∈ interior S ⟷ (∃e>0. ball x e ⊆ S)" using open_contains_ball_eq [where S="interior S"] by (simp add: open_subset_interior) lemma eventually_nhds_in_nhd: "x ∈ interior s ⟹ eventually (λy. y ∈ s) (nhds x)" using interior_subset[of s] by (subst eventually_nhds) blast lemma interior_limit_point [intro]: fixes x :: "'a::perfect_space" assumes x: "x ∈ interior S" shows "x islimpt S" using x islimpt_UNIV [of x] unfolding interior_def islimpt_def apply (clarsimp, rename_tac T T') apply (drule_tac x="T ∩ T'" in spec) apply (auto simp add: open_Int) done lemma interior_closed_Un_empty_interior: assumes cS: "closed S" and iT: "interior T = {}" shows "interior (S ∪ T) = interior S" proof show "interior S ⊆ interior (S ∪ T)" by (rule interior_mono) (rule Un_upper1) show "interior (S ∪ T) ⊆ interior S" proof fix x assume "x ∈ interior (S ∪ T)" then obtain R where "open R" "x ∈ R" "R ⊆ S ∪ T" .. show "x ∈ interior S" proof (rule ccontr) assume "x ∉ interior S" with ‹x ∈ R› ‹open R› obtain y where "y ∈ R - S" unfolding interior_def by fast from ‹open R› ‹closed S› have "open (R - S)" by (rule open_Diff) from ‹R ⊆ S ∪ T› have "R - S ⊆ T" by fast from ‹y ∈ R - S› ‹open (R - S)› ‹R - S ⊆ T› ‹interior T = {}› show False unfolding interior_def by fast qed qed qed lemma interior_Times: "interior (A × B) = interior A × interior B" proof (rule interior_unique) show "interior A × interior B ⊆ A × B" by (intro Sigma_mono interior_subset) show "open (interior A × interior B)" by (intro open_Times open_interior) fix T assume "T ⊆ A × B" and "open T" then show "T ⊆ interior A × interior B" proof safe fix x y assume "(x, y) ∈ T" then obtain C D where "open C" "open D" "C × D ⊆ T" "x ∈ C" "y ∈ D" using ‹open T› unfolding open_prod_def by fast then have "open C" "open D" "C ⊆ A" "D ⊆ B" "x ∈ C" "y ∈ D" using ‹T ⊆ A × B› by auto then show "x ∈ interior A" and "y ∈ interior B" by (auto intro: interiorI) qed qed lemma interior_Ici: fixes x :: "'a :: {dense_linorder, linorder_topology}" assumes "b < x" shows "interior { x ..} = { x <..}" proof (rule interior_unique) fix T assume "T ⊆ {x ..}" "open T" moreover have "x ∉ T" proof assume "x ∈ T" obtain y where "y < x" "{y <.. x} ⊆ T" using open_left[OF ‹open T› ‹x ∈ T› ‹b < x›] by auto with dense[OF ‹y < x›] obtain z where "z ∈ T" "z < x" by (auto simp: subset_eq Ball_def) with ‹T ⊆ {x ..}› show False by auto qed ultimately show "T ⊆ {x <..}" by (auto simp: subset_eq less_le) qed auto lemma interior_Iic: fixes x :: "'a :: {dense_linorder, linorder_topology}" assumes "x < b" shows "interior {.. x} = {..< x}" proof (rule interior_unique) fix T assume "T ⊆ {.. x}" "open T" moreover have "x ∉ T" proof assume "x ∈ T" obtain y where "x < y" "{x ..< y} ⊆ T" using open_right[OF ‹open T› ‹x ∈ T› ‹x < b›] by auto with dense[OF ‹x < y›] obtain z where "z ∈ T" "x < z" by (auto simp: subset_eq Ball_def less_le) with ‹T ⊆ {.. x}› show False by auto qed ultimately show "T ⊆ {..< x}" by (auto simp: subset_eq less_le) qed auto subsection ‹Closure of a Set› definition "closure S = S ∪ {x | x. x islimpt S}" lemma interior_closure: "interior S = - (closure (- S))" unfolding interior_def closure_def islimpt_def by auto lemma closure_interior: "closure S = - interior (- S)" unfolding interior_closure by simp lemma closed_closure[simp, intro]: "closed (closure S)" unfolding closure_interior by (simp add: closed_Compl) lemma closure_subset: "S ⊆ closure S" unfolding closure_def by simp lemma closure_hull: "closure S = closed hull S" unfolding hull_def closure_interior interior_def by auto lemma closure_eq: "closure S = S ⟷ closed S" unfolding closure_hull using closed_Inter by (rule hull_eq) lemma closure_closed [simp]: "closed S ⟹ closure S = S" unfolding closure_eq . lemma closure_closure [simp]: "closure (closure S) = closure S" unfolding closure_hull by (rule hull_hull) lemma closure_mono: "S ⊆ T ⟹ closure S ⊆ closure T" unfolding closure_hull by (rule hull_mono) lemma closure_minimal: "S ⊆ T ⟹ closed T ⟹ closure S ⊆ T" unfolding closure_hull by (rule hull_minimal) lemma closure_unique: assumes "S ⊆ T" and "closed T" and "⋀T'. S ⊆ T' ⟹ closed T' ⟹ T ⊆ T'" shows "closure S = T" using assms unfolding closure_hull by (rule hull_unique) lemma closure_empty [simp]: "closure {} = {}" using closed_empty by (rule closure_closed) lemma closure_UNIV [simp]: "closure UNIV = UNIV" using closed_UNIV by (rule closure_closed) lemma closure_union [simp]: "closure (S ∪ T) = closure S ∪ closure T" unfolding closure_interior by simp lemma closure_eq_empty [iff]: "closure S = {} ⟷ S = {}" using closure_empty closure_subset[of S] by blast lemma closure_subset_eq: "closure S ⊆ S ⟷ closed S" using closure_eq[of S] closure_subset[of S] by simp lemma open_inter_closure_eq_empty: "open S ⟹ (S ∩ closure T) = {} ⟷ S ∩ T = {}" using open_subset_interior[of S "- T"] using interior_subset[of "- T"] unfolding closure_interior by auto lemma open_inter_closure_subset: "open S ⟹ (S ∩ (closure T)) ⊆ closure(S ∩ T)" proof fix x assume as: "open S" "x ∈ S ∩ closure T" { assume *: "x islimpt T" have "x islimpt (S ∩ T)" proof (rule islimptI) fix A assume "x ∈ A" "open A" with as have "x ∈ A ∩ S" "open (A ∩ S)" by (simp_all add: open_Int) with * obtain y where "y ∈ T" "y ∈ A ∩ S" "y ≠ x" by (rule islimptE) then have "y ∈ S ∩ T" "y ∈ A ∧ y ≠ x" by simp_all then show "∃y∈(S ∩ T). y ∈ A ∧ y ≠ x" .. qed } then show "x ∈ closure (S ∩ T)" using as unfolding closure_def by blast qed lemma closure_complement: "closure (- S) = - interior S" unfolding closure_interior by simp lemma interior_complement: "interior (- S) = - closure S" unfolding closure_interior by simp lemma closure_Times: "closure (A × B) = closure A × closure B" proof (rule closure_unique) show "A × B ⊆ closure A × closure B" by (intro Sigma_mono closure_subset) show "closed (closure A × closure B)" by (intro closed_Times closed_closure) fix T assume "A × B ⊆ T" and "closed T" then show "closure A × closure B ⊆ T" apply (simp add: closed_def open_prod_def, clarify) apply (rule ccontr) apply (drule_tac x="(a, b)" in bspec, simp, clarify, rename_tac C D) apply (simp add: closure_interior interior_def) apply (drule_tac x=C in spec) apply (drule_tac x=D in spec) apply auto done qed lemma islimpt_in_closure: "(x islimpt S) = (x:closure(S-{x}))" unfolding closure_def using islimpt_punctured by blast lemma connected_imp_connected_closure: "connected s ⟹ connected (closure s)" by (rule connectedI) (meson closure_subset open_Int open_inter_closure_eq_empty subset_trans connectedD) lemma limpt_of_limpts: fixes x :: "'a::metric_space" shows "x islimpt {y. y islimpt s} ⟹ x islimpt s" apply (clarsimp simp add: islimpt_approachable) apply (drule_tac x="e/2" in spec) apply (auto simp: simp del: less_divide_eq_numeral1) apply (drule_tac x="dist x' x" in spec) apply (auto simp: zero_less_dist_iff simp del: less_divide_eq_numeral1) apply (erule rev_bexI) by (metis dist_commute dist_triangle_half_r less_trans less_irrefl) lemma closed_limpts: "closed {x::'a::metric_space. x islimpt s}" using closed_limpt limpt_of_limpts by blast lemma limpt_of_closure: fixes x :: "'a::metric_space" shows "x islimpt closure s ⟷ x islimpt s" by (auto simp: closure_def islimpt_Un dest: limpt_of_limpts) lemma closed_in_limpt: "closedin (subtopology euclidean t) s ⟷ s ⊆ t ∧ (∀x. x islimpt s ∧ x ∈ t ⟶ x ∈ s)" apply (simp add: closedin_closed, safe) apply (simp add: closed_limpt islimpt_subset) apply (rule_tac x="closure s" in exI) apply simp apply (force simp: closure_def) done lemma closedin_closed_eq: "closed s ⟹ (closedin (subtopology euclidean s) t ⟷ closed t ∧ t ⊆ s)" by (meson closed_in_limpt closed_subset closedin_closed_trans) lemma bdd_below_closure: fixes A :: "real set" assumes "bdd_below A" shows "bdd_below (closure A)" proof - from assms obtain m where "⋀x. x ∈ A ⟹ m ≤ x" unfolding bdd_below_def by auto hence "A ⊆ {m..}" by auto hence "closure A ⊆ {m..}" using closed_real_atLeast by (rule closure_minimal) thus ?thesis unfolding bdd_below_def by auto qed subsection‹Connected components, considered as a connectedness relation or a set› definition "connected_component s x y ≡ ∃t. connected t ∧ t ⊆ s ∧ x ∈ t ∧ y ∈ t" abbreviation "connected_component_set s x ≡ Collect (connected_component s x)" lemma connected_componentI: "⟦connected t; t ⊆ s; x ∈ t; y ∈ t⟧ ⟹ connected_component s x y" by (auto simp: connected_component_def) lemma connected_component_in: "connected_component s x y ⟹ x ∈ s ∧ y ∈ s" by (auto simp: connected_component_def) lemma connected_component_refl: "x ∈ s ⟹ connected_component s x x" apply (auto simp: connected_component_def) using connected_sing by blast lemma connected_component_refl_eq [simp]: "connected_component s x x ⟷ x ∈ s" by (auto simp: connected_component_refl) (auto simp: connected_component_def) lemma connected_component_sym: "connected_component s x y ⟹ connected_component s y x" by (auto simp: connected_component_def) lemma connected_component_trans: "⟦connected_component s x y; connected_component s y z⟧ ⟹ connected_component s x z" unfolding connected_component_def by (metis Int_iff Un_iff Un_subset_iff equals0D connected_Un) lemma connected_component_of_subset: "⟦connected_component s x y; s ⊆ t⟧ ⟹ connected_component t x y" by (auto simp: connected_component_def) lemma connected_component_Union: "connected_component_set s x = ⋃{t. connected t ∧ x ∈ t ∧ t ⊆ s}" by (auto simp: connected_component_def) lemma connected_connected_component [iff]: "connected (connected_component_set s x)" by (auto simp: connected_component_Union intro: connected_Union) lemma connected_iff_eq_connected_component_set: "connected s ⟷ (∀x ∈ s. connected_component_set s x = s)" proof (cases "s={}") case True then show ?thesis by simp next case False then obtain x where "x ∈ s" by auto show ?thesis proof assume "connected s" then show "∀x ∈ s. connected_component_set s x = s" by (force simp: connected_component_def) next assume "∀x ∈ s. connected_component_set s x = s" then show "connected s" by (metis ‹x ∈ s› connected_connected_component) qed qed lemma connected_component_subset: "connected_component_set s x ⊆ s" using connected_component_in by blast lemma connected_component_eq_self: "⟦connected s; x ∈ s⟧ ⟹ connected_component_set s x = s" by (simp add: connected_iff_eq_connected_component_set) lemma connected_iff_connected_component: "connected s ⟷ (∀x ∈ s. ∀y ∈ s. connected_component s x y)" using connected_component_in by (auto simp: connected_iff_eq_connected_component_set) lemma connected_component_maximal: "⟦x ∈ t; connected t; t ⊆ s⟧ ⟹ t ⊆ (connected_component_set s x)" using connected_component_eq_self connected_component_of_subset by blast lemma connected_component_mono: "s ⊆ t ⟹ (connected_component_set s x) ⊆ (connected_component_set t x)" by (simp add: Collect_mono connected_component_of_subset) lemma connected_component_eq_empty [simp]: "connected_component_set s x = {} ⟷ (x ∉ s)" using connected_component_refl by (fastforce simp: connected_component_in) lemma connected_component_set_empty [simp]: "connected_component_set {} x = {}" using connected_component_eq_empty by blast lemma connected_component_eq: "y ∈ connected_component_set s x ⟹ (connected_component_set s y = connected_component_set s x)" by (metis (no_types, lifting) Collect_cong connected_component_sym connected_component_trans mem_Collect_eq) lemma closed_connected_component: assumes s: "closed s" shows "closed (connected_component_set s x)" proof (cases "x ∈ s") case False then show ?thesis by (metis connected_component_eq_empty closed_empty) next case True show ?thesis unfolding closure_eq [symmetric] proof show "closure (connected_component_set s x) ⊆ connected_component_set s x" apply (rule connected_component_maximal) apply (simp add: closure_def True) apply (simp add: connected_imp_connected_closure) apply (simp add: s closure_minimal connected_component_subset) done next show "connected_component_set s x ⊆ closure (connected_component_set s x)" by (simp add: closure_subset) qed qed lemma connected_component_disjoint: "(connected_component_set s a) ∩ (connected_component_set s b) = {} ⟷ a ∉ connected_component_set s b" apply (auto simp: connected_component_eq) using connected_component_eq connected_component_sym by blast lemma connected_component_nonoverlap: "(connected_component_set s a) ∩ (connected_component_set s b) = {} ⟷ (a ∉ s ∨ b ∉ s ∨ connected_component_set s a ≠ connected_component_set s b)" apply (auto simp: connected_component_in) using connected_component_refl_eq apply blast apply (metis connected_component_eq mem_Collect_eq) apply (metis connected_component_eq mem_Collect_eq) done lemma connected_component_overlap: "(connected_component_set s a ∩ connected_component_set s b ≠ {}) = (a ∈ s ∧ b ∈ s ∧ connected_component_set s a = connected_component_set s b)" by (auto simp: connected_component_nonoverlap) lemma connected_component_sym_eq: "connected_component s x y ⟷ connected_component s y x" using connected_component_sym by blast lemma connected_component_eq_eq: "connected_component_set s x = connected_component_set s y ⟷ x ∉ s ∧ y ∉ s ∨ x ∈ s ∧ y ∈ s ∧ connected_component s x y" apply (case_tac "y ∈ s") apply (simp add:) apply (metis connected_component_eq connected_component_eq_empty connected_component_refl_eq mem_Collect_eq) apply (case_tac "x ∈ s") apply (simp add:) apply (metis connected_component_eq_empty) using connected_component_eq_empty by blast lemma connected_iff_connected_component_eq: "connected s ⟷ (∀x ∈ s. ∀y ∈ s. connected_component_set s x = connected_component_set s y)" by (simp add: connected_component_eq_eq connected_iff_connected_component) lemma connected_component_idemp: "connected_component_set (connected_component_set s x) x = connected_component_set s x" apply (rule subset_antisym) apply (simp add: connected_component_subset) by (metis connected_component_eq_empty connected_component_maximal connected_component_refl_eq connected_connected_component mem_Collect_eq set_eq_subset) lemma connected_component_unique: "⟦x ∈ c; c ⊆ s; connected c; ⋀c'. x ∈ c' ∧ c' ⊆ s ∧ connected c' ⟹ c' ⊆ c⟧ ⟹ connected_component_set s x = c" apply (rule subset_antisym) apply (meson connected_component_maximal connected_component_subset connected_connected_component contra_subsetD) by (simp add: connected_component_maximal) lemma joinable_connected_component_eq: "⟦connected t; t ⊆ s; connected_component_set s x ∩ t ≠ {}; connected_component_set s y ∩ t ≠ {}⟧ ⟹ connected_component_set s x = connected_component_set s y" apply (simp add: ex_in_conv [symmetric]) apply (rule connected_component_eq) by (metis (no_types, hide_lams) connected_component_eq_eq connected_component_in connected_component_maximal subsetD mem_Collect_eq) lemma Union_connected_component: "⋃(connected_component_set s ` s) = s" apply (rule subset_antisym) apply (simp add: SUP_least connected_component_subset) using connected_component_refl_eq by force lemma complement_connected_component_unions: "s - connected_component_set s x = ⋃(connected_component_set s ` s - {connected_component_set s x})" apply (subst Union_connected_component [symmetric], auto) apply (metis connected_component_eq_eq connected_component_in) by (metis connected_component_eq mem_Collect_eq) lemma connected_component_intermediate_subset: "⟦connected_component_set u a ⊆ t; t ⊆ u⟧ ⟹ connected_component_set t a = connected_component_set u a" apply (case_tac "a ∈ u") apply (simp add: connected_component_maximal connected_component_mono subset_antisym) using connected_component_eq_empty by blast subsection‹The set of connected components of a set› definition components:: "'a::topological_space set ⇒ 'a set set" where "components s ≡ connected_component_set s ` s" lemma components_iff: "s ∈ components u ⟷ (∃x. x ∈ u ∧ s = connected_component_set u x)" by (auto simp: components_def) lemma Union_components: "u = ⋃(components u)" apply (rule subset_antisym) apply (metis Union_connected_component components_def set_eq_subset) using Union_connected_component components_def by fastforce lemma pairwise_disjoint_components: "pairwise (λX Y. X ∩ Y = {}) (components u)" apply (simp add: pairwise_def) apply (auto simp: components_iff) apply (metis connected_component_eq_eq connected_component_in)+ done lemma in_components_nonempty: "c ∈ components s ⟹ c ≠ {}" by (metis components_iff connected_component_eq_empty) lemma in_components_subset: "c ∈ components s ⟹ c ⊆ s" using Union_components by blast lemma in_components_connected: "c ∈ components s ⟹ connected c" by (metis components_iff connected_connected_component) lemma in_components_maximal: "c ∈ components s ⟷ (c ≠ {} ∧ c ⊆ s ∧ connected c ∧ (∀d. d ≠ {} ∧ c ⊆ d ∧ d ⊆ s ∧ connected d ⟶ d = c))" apply (rule iffI) apply (simp add: in_components_nonempty in_components_connected) apply (metis (full_types) components_iff connected_component_eq_self connected_component_intermediate_subset connected_component_refl in_components_subset mem_Collect_eq rev_subsetD) by (metis bot.extremum_uniqueI components_iff connected_component_eq_empty connected_component_maximal connected_component_subset connected_connected_component subset_emptyI) lemma joinable_components_eq: "connected t ∧ t ⊆ s ∧ c1 ∈ components s ∧ c2 ∈ components s ∧ c1 ∩ t ≠ {} ∧ c2 ∩ t ≠ {} ⟹ c1 = c2" by (metis (full_types) components_iff joinable_connected_component_eq) lemma closed_components: "⟦closed s; c ∈ components s⟧ ⟹ closed c" by (metis closed_connected_component components_iff) lemma components_nonoverlap: "⟦c ∈ components s; c' ∈ components s⟧ ⟹ (c ∩ c' = {}) ⟷ (c ≠ c')" apply (auto simp: in_components_nonempty components_iff) using connected_component_refl apply blast apply (metis connected_component_eq_eq connected_component_in) by (metis connected_component_eq mem_Collect_eq) lemma components_eq: "⟦c ∈ components s; c' ∈ components s⟧ ⟹ (c = c' ⟷ c ∩ c' ≠ {})" by (metis components_nonoverlap) lemma components_eq_empty [simp]: "components s = {} ⟷ s = {}" by (simp add: components_def) lemma components_empty [simp]: "components {} = {}" by simp lemma connected_eq_connected_components_eq: "connected s ⟷ (∀c ∈ components s. ∀c' ∈ components s. c = c')" by (metis (no_types, hide_lams) components_iff connected_component_eq_eq connected_iff_connected_component) lemma components_eq_sing_iff: "components s = {s} ⟷ connected s ∧ s ≠ {}" apply (rule iffI) using in_components_connected apply fastforce apply safe using Union_components apply fastforce apply (metis components_iff connected_component_eq_self) using in_components_maximal by auto lemma components_eq_sing_exists: "(∃a. components s = {a}) ⟷ connected s ∧ s ≠ {}" apply (rule iffI) using connected_eq_connected_components_eq apply fastforce by (metis components_eq_sing_iff) lemma connected_eq_components_subset_sing: "connected s ⟷ components s ⊆ {s}" by (metis Union_components components_empty components_eq_sing_iff connected_empty insert_subset order_refl subset_singletonD) lemma connected_eq_components_subset_sing_exists: "connected s ⟷ (∃a. components s ⊆ {a})" by (metis components_eq_sing_exists connected_eq_components_subset_sing empty_iff subset_iff subset_singletonD) lemma in_components_self: "s ∈ components s ⟷ connected s ∧ s ≠ {}" by (metis components_empty components_eq_sing_iff empty_iff in_components_connected insertI1) lemma components_maximal: "⟦c ∈ components s; connected t; t ⊆ s; c ∩ t ≠ {}⟧ ⟹ t ⊆ c" apply (simp add: components_def ex_in_conv [symmetric], clarify) by (meson connected_component_def connected_component_trans) lemma exists_component_superset: "⟦t ⊆ s; s ≠ {}; connected t⟧ ⟹ ∃c. c ∈ components s ∧ t ⊆ c" apply (case_tac "t = {}") apply force by (metis components_def ex_in_conv connected_component_maximal contra_subsetD image_eqI) lemma components_intermediate_subset: "⟦s ∈ components u; s ⊆ t; t ⊆ u⟧ ⟹ s ∈ components t" apply (auto simp: components_iff) by (metis connected_component_eq_empty connected_component_intermediate_subset) lemma in_components_unions_complement: "c ∈ components s ⟹ s - c = ⋃(components s - {c})" by (metis complement_connected_component_unions components_def components_iff) lemma connected_intermediate_closure: assumes cs: "connected s" and st: "s ⊆ t" and ts: "t ⊆ closure s" shows "connected t" proof (rule connectedI) fix A B assume A: "open A" and B: "open B" and Alap: "A ∩ t ≠ {}" and Blap: "B ∩ t ≠ {}" and disj: "A ∩ B ∩ t = {}" and cover: "t ⊆ A ∪ B" have disjs: "A ∩ B ∩ s = {}" using disj st by auto have "A ∩ closure s ≠ {}" using Alap Int_absorb1 ts by blast then have Alaps: "A ∩ s ≠ {}" by (simp add: A open_inter_closure_eq_empty) have "B ∩ closure s ≠ {}" using Blap Int_absorb1 ts by blast then have Blaps: "B ∩ s ≠ {}" by (simp add: B open_inter_closure_eq_empty) then show False using cs [unfolded connected_def] A B disjs Alaps Blaps cover st by blast qed lemma closed_in_connected_component: "closedin (subtopology euclidean s) (connected_component_set s x)" proof (cases "connected_component_set s x = {}") case True then show ?thesis by (metis closedin_empty) next case False then obtain y where y: "connected_component s x y" by blast have 1: "connected_component_set s x ⊆ s ∩ closure (connected_component_set s x)" by (auto simp: closure_def connected_component_in) have 2: "connected_component s x y ⟹ s ∩ closure (connected_component_set s x) ⊆ connected_component_set s x" apply (rule connected_component_maximal) apply (simp add:) using closure_subset connected_component_in apply fastforce using "1" connected_intermediate_closure apply blast+ done show ?thesis using y apply (simp add: Topology_Euclidean_Space.closedin_closed) using 1 2 by auto qed subsection ‹Frontier (aka boundary)› definition "frontier S = closure S - interior S" lemma frontier_closed: "closed (frontier S)" by (simp add: frontier_def closed_Diff) lemma frontier_closures: "frontier S = (closure S) ∩ (closure(- S))" by (auto simp add: frontier_def interior_closure) lemma frontier_straddle: fixes a :: "'a::metric_space" shows "a ∈ frontier S ⟷ (∀e>0. (∃x∈S. dist a x < e) ∧ (∃x. x ∉ S ∧ dist a x < e))" unfolding frontier_def closure_interior by (auto simp add: mem_interior subset_eq ball_def) lemma frontier_subset_closed: "closed S ⟹ frontier S ⊆ S" by (metis frontier_def closure_closed Diff_subset) lemma frontier_empty[simp]: "frontier {} = {}" by (simp add: frontier_def) lemma frontier_subset_eq: "frontier S ⊆ S ⟷ closed S" proof - { assume "frontier S ⊆ S" then have "closure S ⊆ S" using interior_subset unfolding frontier_def by auto then have "closed S" using closure_subset_eq by auto } then show ?thesis using frontier_subset_closed[of S] .. qed lemma frontier_complement [simp]: "frontier (- S) = frontier S" by (auto simp add: frontier_def closure_complement interior_complement) lemma frontier_disjoint_eq: "frontier S ∩ S = {} ⟷ open S" using frontier_complement frontier_subset_eq[of "- S"] unfolding open_closed by auto subsection ‹Filters and the ``eventually true'' quantifier› definition indirection :: "'a::real_normed_vector ⇒ 'a ⇒ 'a filter" (infixr "indirection" 70) where "a indirection v = at a within {b. ∃c≥0. b - a = scaleR c v}" text ‹Identify Trivial limits, where we can't approach arbitrarily closely.› lemma trivial_limit_within: "trivial_limit (at a within S) ⟷ ¬ a islimpt S" proof assume "trivial_limit (at a within S)" then show "¬ a islimpt S" unfolding trivial_limit_def unfolding eventually_at_topological unfolding islimpt_def apply (clarsimp simp add: set_eq_iff) apply (rename_tac T, rule_tac x=T in exI) apply (clarsimp, drule_tac x=y in bspec, simp_all) done next assume "¬ a islimpt S" then show "trivial_limit (at a within S)" unfolding trivial_limit_def eventually_at_topological islimpt_def by metis qed lemma trivial_limit_at_iff: "trivial_limit (at a) ⟷ ¬ a islimpt UNIV" using trivial_limit_within [of a UNIV] by simp lemma trivial_limit_at: fixes a :: "'a::perfect_space" shows "¬ trivial_limit (at a)" by (rule at_neq_bot) lemma trivial_limit_at_infinity: "¬ trivial_limit (at_infinity :: ('a::{real_normed_vector,perfect_space}) filter)" unfolding trivial_limit_def eventually_at_infinity apply clarsimp apply (subgoal_tac "∃x::'a. x ≠ 0", clarify) apply (rule_tac x="scaleR (b / norm x) x" in exI, simp) apply (cut_tac islimpt_UNIV [of "0::'a", unfolded islimpt_def]) apply (drule_tac x=UNIV in spec, simp) done lemma not_trivial_limit_within: "¬ trivial_limit (at x within S) = (x ∈ closure (S - {x}))" using islimpt_in_closure by (metis trivial_limit_within) lemma at_within_eq_bot_iff: "(at c within A = bot) ⟷ (c ∉ closure (A - {c}))" using not_trivial_limit_within[of c A] by blast text ‹Some property holds "sufficiently close" to the limit point.› lemma trivial_limit_eventually: "trivial_limit net ⟹ eventually P net" by simp lemma trivial_limit_eq: "trivial_limit net ⟷ (∀P. eventually P net)" by (simp add: filter_eq_iff) subsection ‹Limits› lemma Lim: "(f ⤏ l) net ⟷ trivial_limit net ∨ (∀e>0. eventually (λx. dist (f x) l < e) net)" unfolding tendsto_iff trivial_limit_eq by auto text‹Show that they yield usual definitions in the various cases.› lemma Lim_within_le: "(f ⤏ l)(at a within S) ⟷ (∀e>0. ∃d>0. ∀x∈S. 0 < dist x a ∧ dist x a ≤ d ⟶ dist (f x) l < e)" by (auto simp add: tendsto_iff eventually_at_le) lemma Lim_within: "(f ⤏ l) (at a within S) ⟷ (∀e >0. ∃d>0. ∀x ∈ S. 0 < dist x a ∧ dist x a < d ⟶ dist (f x) l < e)" by (auto simp add: tendsto_iff eventually_at) corollary Lim_withinI [intro?]: assumes "⋀e. e > 0 ⟹ ∃d>0. ∀x ∈ S. 0 < dist x a ∧ dist x a < d ⟶ dist (f x) l ≤ e" shows "(f ⤏ l) (at a within S)" apply (simp add: Lim_within, clarify) apply (rule ex_forward [OF assms [OF half_gt_zero]], auto) done lemma Lim_at: "(f ⤏ l) (at a) ⟷ (∀e >0. ∃d>0. ∀x. 0 < dist x a ∧ dist x a < d ⟶ dist (f x) l < e)" by (auto simp add: tendsto_iff eventually_at2) lemma Lim_at_infinity: "(f ⤏ l) at_infinity ⟷ (∀e>0. ∃b. ∀x. norm x ≥ b ⟶ dist (f x) l < e)" by (auto simp add: tendsto_iff eventually_at_infinity) corollary Lim_at_infinityI [intro?]: assumes "⋀e. e > 0 ⟹ ∃B. ∀x. norm x ≥ B ⟶ dist (f x) l ≤ e" shows "(f ⤏ l) at_infinity" apply (simp add: Lim_at_infinity, clarify) apply (rule ex_forward [OF assms [OF half_gt_zero]], auto) done lemma Lim_eventually: "eventually (λx. f x = l) net ⟹ (f ⤏ l) net" by (rule topological_tendstoI, auto elim: eventually_mono) text‹The expected monotonicity property.› lemma Lim_Un: assumes "(f ⤏ l) (at x within S)" "(f ⤏ l) (at x within T)" shows "(f ⤏ l) (at x within (S ∪ T))" using assms unfolding at_within_union by (rule filterlim_sup) lemma Lim_Un_univ: "(f ⤏ l) (at x within S) ⟹ (f ⤏ l) (at x within T) ⟹ S ∪ T = UNIV ⟹ (f ⤏ l) (at x)" by (metis Lim_Un) text‹Interrelations between restricted and unrestricted limits.› lemma Lim_at_imp_Lim_at_within: "(f ⤏ l) (at x) ⟹ (f ⤏ l) (at x within S)" by (metis order_refl filterlim_mono subset_UNIV at_le) lemma eventually_within_interior: assumes "x ∈ interior S" shows "eventually P (at x within S) ⟷ eventually P (at x)" (is "?lhs = ?rhs") proof from assms obtain T where T: "open T" "x ∈ T" "T ⊆ S" .. { assume "?lhs" then obtain A where "open A" and "x ∈ A" and "∀y∈A. y ≠ x ⟶ y ∈ S ⟶ P y" unfolding eventually_at_topological by auto with T have "open (A ∩ T)" and "x ∈ A ∩ T" and "∀y ∈ A ∩ T. y ≠ x ⟶ P y" by auto then show "?rhs" unfolding eventually_at_topological by auto next assume "?rhs" then show "?lhs" by (auto elim: eventually_mono simp: eventually_at_filter) } qed lemma at_within_interior: "x ∈ interior S ⟹ at x within S = at x" unfolding filter_eq_iff by (intro allI eventually_within_interior) lemma Lim_within_LIMSEQ: fixes a :: "'a::first_countable_topology" assumes "∀S. (∀n. S n ≠ a ∧ S n ∈ T) ∧ S ⇢ a ⟶ (λn. X (S n)) ⇢ L" shows "(X ⤏ L) (at a within T)" using assms unfolding tendsto_def [where l=L] by (simp add: sequentially_imp_eventually_within) lemma Lim_right_bound: fixes f :: "'a :: {linorder_topology, conditionally_complete_linorder, no_top} ⇒ 'b::{linorder_topology, conditionally_complete_linorder}" assumes mono: "⋀a b. a ∈ I ⟹ b ∈ I ⟹ x < a ⟹ a ≤ b ⟹ f a ≤ f b" and bnd: "⋀a. a ∈ I ⟹ x < a ⟹ K ≤ f a" shows "(f ⤏ Inf (f ` ({x<..} ∩ I))) (at x within ({x<..} ∩ I))" proof (cases "{x<..} ∩ I = {}") case True then show ?thesis by simp next case False show ?thesis proof (rule order_tendstoI) fix a assume a: "a < Inf (f ` ({x<..} ∩ I))" { fix y assume "y ∈ {x<..} ∩ I" with False bnd have "Inf (f ` ({x<..} ∩ I)) ≤ f y" by (auto intro!: cInf_lower bdd_belowI2 simp del: Inf_image_eq) with a have "a < f y" by (blast intro: less_le_trans) } then show "eventually (λx. a < f x) (at x within ({x<..} ∩ I))" by (auto simp: eventually_at_filter intro: exI[of _ 1] zero_less_one) next fix a assume "Inf (f ` ({x<..} ∩ I)) < a" from cInf_lessD[OF _ this] False obtain y where y: "x < y" "y ∈ I" "f y < a" by auto then have "eventually (λx. x ∈ I ⟶ f x < a) (at_right x)" unfolding eventually_at_right[OF ‹x < y›] by (metis less_imp_le le_less_trans mono) then show "eventually (λx. f x < a) (at x within ({x<..} ∩ I))" unfolding eventually_at_filter by eventually_elim simp qed qed text‹Another limit point characterization.› lemma islimpt_sequential: fixes x :: "'a::first_countable_topology" shows "x islimpt S ⟷ (∃f. (∀n::nat. f n ∈ S - {x}) ∧ (f ⤏ x) sequentially)" (is "?lhs = ?rhs") proof assume ?lhs from countable_basis_at_decseq[of x] obtain A where A: "⋀i. open (A i)" "⋀i. x ∈ A i" "⋀S. open S ⟹ x ∈ S ⟹ eventually (λi. A i ⊆ S) sequentially" by blast def f ≡ "λn. SOME y. y ∈ S ∧ y ∈ A n ∧ x ≠ y" { fix n from ‹?lhs› have "∃y. y ∈ S ∧ y ∈ A n ∧ x ≠ y" unfolding islimpt_def using A(1,2)[of n] by auto then have "f n ∈ S ∧ f n ∈ A n ∧ x ≠ f n" unfolding f_def by (rule someI_ex) then have "f n ∈ S" "f n ∈ A n" "x ≠ f n" by auto } then have "∀n. f n ∈ S - {x}" by auto moreover have "(λn. f n) ⇢ x" proof (rule topological_tendstoI) fix S assume "open S" "x ∈ S" from A(3)[OF this] ‹⋀n. f n ∈ A n› show "eventually (λx. f x ∈ S) sequentially" by (auto elim!: eventually_mono) qed ultimately show ?rhs by fast next assume ?rhs then obtain f :: "nat ⇒ 'a" where f: "⋀n. f n ∈ S - {x}" and lim: "f ⇢ x" by auto show ?lhs unfolding islimpt_def proof safe fix T assume "open T" "x ∈ T" from lim[THEN topological_tendstoD, OF this] f show "∃y∈S. y ∈ T ∧ y ≠ x" unfolding eventually_sequentially by auto qed qed lemma Lim_null: fixes f :: "'a ⇒ 'b::real_normed_vector" shows "(f ⤏ l) net ⟷ ((λx. f(x) - l) ⤏ 0) net" by (simp add: Lim dist_norm) lemma Lim_null_comparison: fixes f :: "'a ⇒ 'b::real_normed_vector" assumes "eventually (λx. norm (f x) ≤ g x) net" "(g ⤏ 0) net" shows "(f ⤏ 0) net" using assms(2) proof (rule metric_tendsto_imp_tendsto) show "eventually (λx. dist (f x) 0 ≤ dist (g x) 0) net" using assms(1) by (rule eventually_mono) (simp add: dist_norm) qed lemma Lim_transform_bound: fixes f :: "'a ⇒ 'b::real_normed_vector" and g :: "'a ⇒ 'c::real_normed_vector" assumes "eventually (λn. norm (f n) ≤ norm (g n)) net" and "(g ⤏ 0) net" shows "(f ⤏ 0) net" using assms(1) tendsto_norm_zero [OF assms(2)] by (rule Lim_null_comparison) text‹Deducing things about the limit from the elements.› lemma Lim_in_closed_set: assumes "closed S" and "eventually (λx. f(x) ∈ S) net" and "¬ trivial_limit net" "(f ⤏ l) net" shows "l ∈ S" proof (rule ccontr) assume "l ∉ S" with ‹closed S› have "open (- S)" "l ∈ - S" by (simp_all add: open_Compl) with assms(4) have "eventually (λx. f x ∈ - S) net" by (rule topological_tendstoD) with assms(2) have "eventually (λx. False) net" by (rule eventually_elim2) simp with assms(3) show "False" by (simp add: eventually_False) qed text‹Need to prove closed(cball(x,e)) before deducing this as a corollary.› lemma Lim_dist_ubound: assumes "¬(trivial_limit net)" and "(f ⤏ l) net" and "eventually (λx. dist a (f x) ≤ e) net" shows "dist a l ≤ e" using assms by (fast intro: tendsto_le tendsto_intros) lemma Lim_norm_ubound: fixes f :: "'a ⇒ 'b::real_normed_vector" assumes "¬(trivial_limit net)" "(f ⤏ l) net" "eventually (λx. norm(f x) ≤ e) net" shows "norm(l) ≤ e" using assms by (fast intro: tendsto_le tendsto_intros) lemma Lim_norm_lbound: fixes f :: "'a ⇒ 'b::real_normed_vector" assumes "¬ trivial_limit net" and "(f ⤏ l) net" and "eventually (λx. e ≤ norm (f x)) net" shows "e ≤ norm l" using assms by (fast intro: tendsto_le tendsto_intros) text‹Limit under bilinear function› lemma Lim_bilinear: assumes "(f ⤏ l) net" and "(g ⤏ m) net" and "bounded_bilinear h" shows "((λx. h (f x) (g x)) ⤏ (h l m)) net" using ‹bounded_bilinear h› ‹(f ⤏ l) net› ‹(g ⤏ m) net› by (rule bounded_bilinear.tendsto) text‹These are special for limits out of the same vector space.› lemma Lim_within_id: "(id ⤏ a) (at a within s)" unfolding id_def by (rule tendsto_ident_at) lemma Lim_at_id: "(id ⤏ a) (at a)" unfolding id_def by (rule tendsto_ident_at) lemma Lim_at_zero: fixes a :: "'a::real_normed_vector" and l :: "'b::topological_space" shows "(f ⤏ l) (at a) ⟷ ((λx. f(a + x)) ⤏ l) (at 0)" using LIM_offset_zero LIM_offset_zero_cancel .. text‹It's also sometimes useful to extract the limit point from the filter.› abbreviation netlimit :: "'a::t2_space filter ⇒ 'a" where "netlimit F ≡ Lim F (λx. x)" lemma netlimit_within: "¬ trivial_limit (at a within S) ⟹ netlimit (at a within S) = a" by (rule tendsto_Lim) (auto intro: tendsto_intros) lemma netlimit_at: fixes a :: "'a::{perfect_space,t2_space}" shows "netlimit (at a) = a" using netlimit_within [of a UNIV] by simp lemma lim_within_interior: "x ∈ interior S ⟹ (f ⤏ l) (at x within S) ⟷ (f ⤏ l) (at x)" by (metis at_within_interior) lemma netlimit_within_interior: fixes x :: "'a::{t2_space,perfect_space}" assumes "x ∈ interior S" shows "netlimit (at x within S) = x" using assms by (metis at_within_interior netlimit_at) lemma netlimit_at_vector: fixes a :: "'a::real_normed_vector" shows "netlimit (at a) = a" proof (cases "∃x. x ≠ a") case True then obtain x where x: "x ≠ a" .. have "¬ trivial_limit (at a)" unfolding trivial_limit_def eventually_at dist_norm apply clarsimp apply (rule_tac x="a + scaleR (d / 2) (sgn (x - a))" in exI) apply (simp add: norm_sgn sgn_zero_iff x) done then show ?thesis by (rule netlimit_within [of a UNIV]) qed simp text‹Useful lemmas on closure and set of possible sequential limits.› lemma closure_sequential: fixes l :: "'a::first_countable_topology" shows "l ∈ closure S ⟷ (∃x. (∀n. x n ∈ S) ∧ (x ⤏ l) sequentially)" (is "?lhs = ?rhs") proof assume "?lhs" moreover { assume "l ∈ S" then have "?rhs" using tendsto_const[of l sequentially] by auto } moreover { assume "l islimpt S" then have "?rhs" unfolding islimpt_sequential by auto } ultimately show "?rhs" unfolding closure_def by auto next assume "?rhs" then show "?lhs" unfolding closure_def islimpt_sequential by auto qed lemma closed_sequential_limits: fixes S :: "'a::first_countable_topology set" shows "closed S ⟷ (∀x l. (∀n. x n ∈ S) ∧ (x ⤏ l) sequentially ⟶ l ∈ S)" by (metis closure_sequential closure_subset_eq subset_iff) lemma closure_approachable: fixes S :: "'a::metric_space set" shows "x ∈ closure S ⟷ (∀e>0. ∃y∈S. dist y x < e)" apply (auto simp add: closure_def islimpt_approachable) apply (metis dist_self) done lemma closed_approachable: fixes S :: "'a::metric_space set" shows "closed S ⟹ (∀e>0. ∃y∈S. dist y x < e) ⟷ x ∈ S" by (metis closure_closed closure_approachable) lemma closure_contains_Inf: fixes S :: "real set" assumes "S ≠ {}" "bdd_below S" shows "Inf S ∈ closure S" proof - have *: "∀x∈S. Inf S ≤ x" using cInf_lower[of _ S] assms by metis { fix e :: real assume "e > 0" then have "Inf S < Inf S + e" by simp with assms obtain x where "x ∈ S" "x < Inf S + e" by (subst (asm) cInf_less_iff) auto with * have "∃x∈S. dist x (Inf S) < e" by (intro bexI[of _ x]) (auto simp add: dist_real_def) } then show ?thesis unfolding closure_approachable by auto qed lemma closed_contains_Inf: fixes S :: "real set" shows "S ≠ {} ⟹ bdd_below S ⟹ closed S ⟹ Inf S ∈ S" by (metis closure_contains_Inf closure_closed assms) lemma closed_subset_contains_Inf: fixes A C :: "real set" shows "closed C ⟹ A ⊆ C ⟹ A ≠ {} ⟹ bdd_below A ⟹ Inf A ∈ C" by (metis closure_contains_Inf closure_minimal subset_eq) lemma atLeastAtMost_subset_contains_Inf: fixes A :: "real set" and a b :: real shows "A ≠ {} ⟹ a ≤ b ⟹ A ⊆ {a..b} ⟹ Inf A ∈ {a..b}" by (rule closed_subset_contains_Inf) (auto intro: closed_real_atLeastAtMost intro!: bdd_belowI[of A a]) lemma not_trivial_limit_within_ball: "¬ trivial_limit (at x within S) ⟷ (∀e>0. S ∩ ball x e - {x} ≠ {})" (is "?lhs ⟷ ?rhs") proof show ?rhs if ?lhs proof - { fix e :: real assume "e > 0" then obtain y where "y ∈ S - {x}" and "dist y x < e" using ‹?lhs› not_trivial_limit_within[of x S] closure_approachable[of x "S - {x}"] by auto then have "y ∈ S ∩ ball x e - {x}" unfolding ball_def by (simp add: dist_commute) then have "S ∩ ball x e - {x} ≠ {}" by blast } then show ?thesis by auto qed show ?lhs if ?rhs proof - { fix e :: real assume "e > 0" then obtain y where "y ∈ S ∩ ball x e - {x}" using ‹?rhs› by blast then have "y ∈ S - {x}" and "dist y x < e" unfolding ball_def by (simp_all add: dist_commute) then have "∃y ∈ S - {x}. dist y x < e" by auto } then show ?thesis using not_trivial_limit_within[of x S] closure_approachable[of x "S - {x}"] by auto qed qed subsection ‹Infimum Distance› definition "infdist x A = (if A = {} then 0 else INF a:A. dist x a)" lemma bdd_below_infdist[intro, simp]: "bdd_below (dist x`A)" by (auto intro!: zero_le_dist) lemma infdist_notempty: "A ≠ {} ⟹ infdist x A = (INF a:A. dist x a)" by (simp add: infdist_def) lemma infdist_nonneg: "0 ≤ infdist x A" by (auto simp add: infdist_def intro: cINF_greatest) lemma infdist_le: "a ∈ A ⟹ infdist x A ≤ dist x a" by (auto intro: cINF_lower simp add: infdist_def) lemma infdist_le2: "a ∈ A ⟹ dist x a ≤ d ⟹ infdist x A ≤ d" by (auto intro!: cINF_lower2 simp add: infdist_def) lemma infdist_zero[simp]: "a ∈ A ⟹ infdist a A = 0" by (auto intro!: antisym infdist_nonneg infdist_le2) lemma infdist_triangle: "infdist x A ≤ infdist y A + dist x y" proof (cases "A = {}") case True then show ?thesis by (simp add: infdist_def) next case False then obtain a where "a ∈ A" by auto have "infdist x A ≤ Inf {dist x y + dist y a |a. a ∈ A}" proof (rule cInf_greatest) from ‹A ≠ {}› show "{dist x y + dist y a |a. a ∈ A} ≠ {}" by simp fix d assume "d ∈ {dist x y + dist y a |a. a ∈ A}" then obtain a where d: "d = dist x y + dist y a" "a ∈ A" by auto show "infdist x A ≤ d" unfolding infdist_notempty[OF ‹A ≠ {}›] proof (rule cINF_lower2) show "a ∈ A" by fact show "dist x a ≤ d" unfolding d by (rule dist_triangle) qed simp qed also have "… = dist x y + infdist y A" proof (rule cInf_eq, safe) fix a assume "a ∈ A" then show "dist x y + infdist y A ≤ dist x y + dist y a" by (auto intro: infdist_le) next fix i assume inf: "⋀d. d ∈ {dist x y + dist y a |a. a ∈ A} ⟹ i ≤ d" then have "i - dist x y ≤ infdist y A" unfolding infdist_notempty[OF ‹A ≠ {}›] using ‹a ∈ A› by (intro cINF_greatest) (auto simp: field_simps) then show "i ≤ dist x y + infdist y A" by simp qed finally show ?thesis by simp qed lemma in_closure_iff_infdist_zero: assumes "A ≠ {}" shows "x ∈ closure A ⟷ infdist x A = 0" proof assume "x ∈ closure A" show "infdist x A = 0" proof (rule ccontr) assume "infdist x A ≠ 0" with infdist_nonneg[of x A] have "infdist x A > 0" by auto then have "ball x (infdist x A) ∩ closure A = {}" apply auto apply (metis ‹x ∈ closure A› closure_approachable dist_commute infdist_le not_less) done then have "x ∉ closure A" by (metis ‹0 < infdist x A› centre_in_ball disjoint_iff_not_equal) then show False using ‹x ∈ closure A› by simp qed next assume x: "infdist x A = 0" then obtain a where "a ∈ A" by atomize_elim (metis all_not_in_conv assms) show "x ∈ closure A" unfolding closure_approachable apply safe proof (rule ccontr) fix e :: real assume "e > 0" assume "¬ (∃y∈A. dist y x < e)" then have "infdist x A ≥ e" using ‹a ∈ A› unfolding infdist_def by (force simp: dist_commute intro: cINF_greatest) with x ‹e > 0› show False by auto qed qed lemma in_closed_iff_infdist_zero: assumes "closed A" "A ≠ {}" shows "x ∈ A ⟷ infdist x A = 0" proof - have "x ∈ closure A ⟷ infdist x A = 0" by (rule in_closure_iff_infdist_zero) fact with assms show ?thesis by simp qed lemma tendsto_infdist [tendsto_intros]: assumes f: "(f ⤏ l) F" shows "((λx. infdist (f x) A) ⤏ infdist l A) F" proof (rule tendstoI) fix e ::real assume "e > 0" from tendstoD[OF f this] show "eventually (λx. dist (infdist (f x) A) (infdist l A) < e) F" proof (eventually_elim) fix x from infdist_triangle[of l A "f x"] infdist_triangle[of "f x" A l] have "dist (infdist (f x) A) (infdist l A) ≤ dist (f x) l" by (simp add: dist_commute dist_real_def) also assume "dist (f x) l < e" finally show "dist (infdist (f x) A) (infdist l A) < e" . qed qed text‹Some other lemmas about sequences.› lemma sequentially_offset: (* TODO: move to Topological_Spaces.thy *) assumes "eventually (λi. P i) sequentially" shows "eventually (λi. P (i + k)) sequentially" using assms by (rule eventually_sequentially_seg [THEN iffD2]) lemma seq_offset_neg: (* TODO: move to Topological_Spaces.thy *) "(f ⤏ l) sequentially ⟹ ((λi. f(i - k)) ⤏ l) sequentially" apply (erule filterlim_compose) apply (simp add: filterlim_def le_sequentially eventually_filtermap eventually_sequentially) apply arith done lemma seq_harmonic: "((λn. inverse (real n)) ⤏ 0) sequentially" using LIMSEQ_inverse_real_of_nat by (rule LIMSEQ_imp_Suc) (* TODO: move to Limits.thy *) subsection ‹More properties of closed balls› lemma closed_cball [iff]: "closed (cball x e)" proof - have "closed (dist x -` {..e})" by (intro closed_vimage closed_atMost continuous_intros) also have "dist x -` {..e} = cball x e" by auto finally show ?thesis . qed lemma open_contains_cball: "open S ⟷ (∀x∈S. ∃e>0. cball x e ⊆ S)" proof - { fix x and e::real assume "x∈S" "e>0" "ball x e ⊆ S" then have "∃d>0. cball x d ⊆ S" unfolding subset_eq by (rule_tac x="e/2" in exI, auto) } moreover { fix x and e::real assume "x∈S" "e>0" "cball x e ⊆ S" then have "∃d>0. ball x d ⊆ S" unfolding subset_eq apply(rule_tac x="e/2" in exI) apply auto done } ultimately show ?thesis unfolding open_contains_ball by auto qed lemma open_contains_cball_eq: "open S ⟹ (∀x. x ∈ S ⟷ (∃e>0. cball x e ⊆ S))" by (metis open_contains_cball subset_eq order_less_imp_le centre_in_cball) lemma mem_interior_cball: "x ∈ interior S ⟷ (∃e>0. cball x e ⊆ S)" apply (simp add: interior_def, safe) apply (force simp add: open_contains_cball) apply (rule_tac x="ball x e" in exI) apply (simp add: subset_trans [OF ball_subset_cball]) done lemma islimpt_ball: fixes x y :: "'a::{real_normed_vector,perfect_space}" shows "y islimpt ball x e ⟷ 0 < e ∧ y ∈ cball x e" (is "?lhs ⟷ ?rhs") proof show ?rhs if ?lhs proof { assume "e ≤ 0" then have *: "ball x e = {}" using ball_eq_empty[of x e] by auto have False using ‹?lhs› unfolding * using islimpt_EMPTY[of y] by auto } then show "e > 0" by (metis not_less) show "y ∈ cball x e" using closed_cball[of x e] islimpt_subset[of y "ball x e" "cball x e"] ball_subset_cball[of x e] ‹?lhs› unfolding closed_limpt by auto qed show ?lhs if ?rhs proof - from that have "e > 0" by auto { fix d :: real assume "d > 0" have "∃x'∈ball x e. x' ≠ y ∧ dist x' y < d" proof (cases "d ≤ dist x y") case True then show "∃x'∈ball x e. x' ≠ y ∧ dist x' y < d" proof (cases "x = y") case True then have False using ‹d ≤ dist x y› ‹d>0› by auto then show "∃x'∈ball x e. x' ≠ y ∧ dist x' y < d" by auto next case False have "dist x (y - (d / (2 * dist y x)) *⇩_{R}(y - x)) = norm (x - y + (d / (2 * norm (y - x))) *⇩_{R}(y - x))" unfolding mem_cball mem_ball dist_norm diff_diff_eq2 diff_add_eq[symmetric] by auto also have "… = ¦- 1 + d / (2 * norm (x - y))¦ * norm (x - y)" using scaleR_left_distrib[of "- 1" "d / (2 * norm (y - x))", symmetric, of "y - x"] unfolding scaleR_minus_left scaleR_one by (auto simp add: norm_minus_commute) also have "… = ¦- norm (x - y) + d / 2¦" unfolding abs_mult_pos[of "norm (x - y)", OF norm_ge_zero[of "x - y"]] unfolding distrib_right using ‹x≠y› by auto also have "… ≤ e - d/2" using ‹d ≤ dist x y› and ‹d>0› and ‹?rhs› by (auto simp add: dist_norm) finally have "y - (d / (2 * dist y x)) *⇩_{R}(y - x) ∈ ball x e" using ‹d>0› by auto moreover have "(d / (2*dist y x)) *⇩_{R}(y - x) ≠ 0" using ‹x≠y›[unfolded dist_nz] ‹d>0› unfolding scaleR_eq_0_iff by (auto simp add: dist_commute) moreover have "dist (y - (d / (2 * dist y x)) *⇩_{R}(y - x)) y < d" unfolding dist_norm apply simp unfolding norm_minus_cancel using ‹d > 0› ‹x≠y›[unfolded dist_nz] dist_commute[of x y] unfolding dist_norm apply auto done ultimately show "∃x'∈ball x e. x' ≠ y ∧ dist x' y < d" apply (rule_tac x = "y - (d / (2*dist y x)) *⇩_{R}(y - x)" in bexI) apply auto done qed next case False then have "d > dist x y" by auto show "∃x' ∈ ball x e. x' ≠ y ∧ dist x' y < d" proof (cases "x = y") case True obtain z where **: "z ≠ y" "dist z y < min e d" using perfect_choose_dist[of "min e d" y] using ‹d > 0› ‹e>0› by auto show "∃x'∈ball x e. x' ≠ y ∧ dist x' y < d" unfolding ‹x = y› using ‹z ≠ y› ** apply (rule_tac x=z in bexI) apply (auto simp add: dist_commute) done next case False then show "∃x'∈ball x e. x' ≠ y ∧ dist x' y < d" using ‹d>0› ‹d > dist x y› ‹?rhs› apply (rule_tac x=x in bexI) apply auto done qed qed } then show ?thesis unfolding mem_cball islimpt_approachable mem_ball by auto qed qed lemma closure_ball_lemma: fixes x y :: "'a::real_normed_vector" assumes "x ≠ y" shows "y islimpt ball x (dist x y)" proof (rule islimptI) fix T assume "y ∈ T" "open T" then obtain r where "0 < r" "∀z. dist z y < r ⟶ z ∈ T" unfolding open_dist by fast (* choose point between x and y, within distance r of y. *) def k ≡ "min 1 (r / (2 * dist x y))" def z ≡ "y + scaleR k (x - y)" have z_def2: "z = x + scaleR (1 - k) (y - x)" unfolding z_def by (simp add: algebra_simps) have "dist z y < r" unfolding z_def k_def using ‹0 < r› by (simp add: dist_norm min_def) then have "z ∈ T" using ‹∀z. dist z y < r ⟶ z ∈ T› by simp have "dist x z < dist x y" unfolding z_def2 dist_norm apply (simp add: norm_minus_commute) apply (simp only: dist_norm [symmetric]) apply (subgoal_tac "¦1 - k¦ * dist x y < 1 * dist x y", simp) apply (rule mult_strict_right_mono) apply (simp add: k_def ‹0 < r› ‹x ≠ y›) apply (simp add: ‹x ≠ y›) done then have "z ∈ ball x (dist x y)" by simp have "z ≠ y" unfolding z_def k_def using ‹x ≠ y› ‹0 < r› by (simp add: min_def) show "∃z∈ball x (dist x y). z ∈ T ∧ z ≠ y" using ‹z ∈ ball x (dist x y)› ‹z ∈ T› ‹z ≠ y› by fast qed lemma closure_ball [simp]: fixes x :: "'a::real_normed_vector" shows "0 < e ⟹ closure (ball x e) = cball x e" apply (rule equalityI) apply (rule closure_minimal) apply (rule ball_subset_cball) apply (rule closed_cball) apply (rule subsetI, rename_tac y) apply (simp add: le_less [where 'a=real]) apply (erule disjE) apply (rule subsetD [OF closure_subset], simp) apply (simp add: closure_def) apply clarify apply (rule closure_ball_lemma) apply (simp add: zero_less_dist_iff) done (* In a trivial vector space, this fails for e = 0. *) lemma interior_cball [simp]: fixes x :: "'a::{real_normed_vector, perfect_space}" shows "interior (cball x e) = ball x e" proof (cases "e ≥ 0") case False note cs = this from cs have null: "ball x e = {}" using ball_empty[of e x] by auto moreover { fix y assume "y ∈ cball x e" then have False by (metis ball_eq_empty null cs dist_eq_0_iff dist_le_zero_iff empty_subsetI mem_cball subset_antisym subset_ball) } then have "cball x e = {}" by auto then have "interior (cball x e) = {}" using interior_empty by auto ultimately show ?thesis by blast next case True note cs = this have "ball x e ⊆ cball x e" using ball_subset_cball by auto moreover { fix S y assume as: "S ⊆ cball x e" "open S" "y∈S" then obtain d where "d>0" and d: "∀x'. dist x' y < d ⟶ x' ∈ S" unfolding open_dist by blast then obtain xa where xa_y: "xa ≠ y" and xa: "dist xa y < d" using perfect_choose_dist [of d] by auto have "xa ∈ S" using d[THEN spec[where x = xa]] using xa by (auto simp add: dist_commute) then have xa_cball: "xa ∈ cball x e" using as(1) by auto then have "y ∈ ball x e" proof (cases "x = y") case True then have "e > 0" using cs order.order_iff_strict xa_cball xa_y by fastforce then show "y ∈ ball x e" using ‹x = y › by simp next case False have "dist (y + (d / 2 / dist y x) *⇩_{R}(y - x)) y < d" unfolding dist_norm using ‹d>0› norm_ge_zero[of "y - x"] ‹x ≠ y› by auto then have *: "y + (d / 2 / dist y x) *⇩_{R}(y - x) ∈ cball x e" using d as(1)[unfolded subset_eq] by blast have "y - x ≠ 0" using ‹x ≠ y› by auto hence **:"d / (2 * norm (y - x)) > 0" unfolding zero_less_norm_iff[symmetric] using ‹d>0› by auto have "dist (y + (d / 2 / dist y x) *⇩_{R}(y - x)) x = norm (y + (d / (2 * norm (y - x))) *⇩_{R}y - (d / (2 * norm (y - x))) *⇩_{R}x - x)" by (auto simp add: dist_norm algebra_simps) also have "… = norm ((1 + d / (2 * norm (y - x))) *⇩_{R}(y - x))" by (auto simp add: algebra_simps) also have "… = ¦1 + d / (2 * norm (y - x))¦ * norm (y - x)" using ** by auto also have "… = (dist y x) + d/2" using ** by (auto simp add: distrib_right dist_norm) finally have "e ≥ dist x y +d/2" using *[unfolded mem_cball] by (auto simp add: dist_commute) then show "y ∈ ball x e" unfolding mem_ball using ‹d>0› by auto qed } then have "∀S ⊆ cball x e. open S ⟶ S ⊆ ball x e" by auto ultimately show ?thesis using interior_unique[of "ball x e" "cball x e"] using open_ball[of x e] by auto qed lemma frontier_ball: fixes a :: "'a::real_normed_vector" shows "0 < e ⟹ frontier(ball a e) = {x. dist a x = e}" apply (simp add: frontier_def closure_ball interior_open order_less_imp_le) apply (simp add: set_eq_iff) apply arith done lemma frontier_cball: fixes a :: "'a::{real_normed_vector, perfect_space}" shows "frontier (cball a e) = {x. dist a x = e}" apply (simp add: frontier_def interior_cball closed_cball order_less_imp_le) apply (simp add: set_eq_iff) apply arith done lemma cball_eq_empty [simp]: "cball x e = {} ⟷ e < 0" apply (simp add: set_eq_iff not_le) apply (metis zero_le_dist dist_self order_less_le_trans) done lemma cball_empty [simp]: "e < 0 ⟹ cball x e = {}" by (simp add: cball_eq_empty) lemma cball_eq_sing: fixes x :: "'a::{metric_space,perfect_space}" shows "cball x e = {x} ⟷ e = 0" proof (rule linorder_cases) assume e: "0 < e" obtain a where "a ≠ x" "dist a x < e" using perfect_choose_dist [OF e] by auto then have "a ≠ x" "dist x a ≤ e" by (auto simp add: dist_commute) with e show ?thesis by (auto simp add: set_eq_iff) qed auto lemma cball_sing: fixes x :: "'a::metric_space" shows "e = 0 ⟹ cball x e = {x}" by (auto simp add: set_eq_iff) lemma ball_divide_subset: "d ≥ 1 ⟹ ball x (e/d) ⊆ ball x e" apply (cases "e ≤ 0") apply (simp add: ball_empty divide_simps) apply (rule subset_ball) apply (simp add: divide_simps) done lemma ball_divide_subset_numeral: "ball x (e / numeral w) ⊆ ball x e" using ball_divide_subset one_le_numeral by blast lemma cball_divide_subset: "d ≥ 1 ⟹ cball x (e/d) ⊆ cball x e" apply (cases "e < 0") apply (simp add: divide_simps) apply (rule subset_cball) apply (metis divide_1 frac_le not_le order_refl zero_less_one) done lemma cball_divide_subset_numeral: "cball x (e / numeral w) ⊆ cball x e" using cball_divide_subset one_le_numeral by blast subsection ‹Boundedness› (* FIXME: This has to be unified with BSEQ!! *) definition (in metric_space) bounded :: "'a set ⇒ bool" where "bounded S ⟷ (∃x e. ∀y∈S. dist x y ≤ e)" lemma bounded_subset_cball: "bounded S ⟷ (∃e x. S ⊆ cball x e ∧ 0 ≤ e)" unfolding bounded_def subset_eq by auto (meson order_trans zero_le_dist) lemma bounded_subset_ballD: assumes "bounded S" shows "∃r. 0 < r ∧ S ⊆ ball x r" proof - obtain e::real and y where "S ⊆ cball y e" "0 ≤ e" using assms by (auto simp: bounded_subset_cball) then show ?thesis apply (rule_tac x="dist x y + e + 1" in exI) apply (simp add: add.commute add_pos_nonneg) apply (erule subset_trans) apply (clarsimp simp add: cball_def) by (metis add_le_cancel_right add_strict_increasing dist_commute dist_triangle_le zero_less_one) qed lemma bounded_any_center: "bounded S ⟷ (∃e. ∀y∈S. dist a y ≤ e)" unfolding bounded_def by auto (metis add.commute add_le_cancel_right dist_commute dist_triangle_le) lemma bounded_iff: "bounded S ⟷ (∃a. ∀x∈S. norm x ≤ a)" unfolding bounded_any_center [where a=0] by (simp add: dist_norm) lemma bdd_above_norm: "bdd_above (norm ` X) ⟷ bounded X" by (simp add: bounded_iff bdd_above_def) lemma bounded_realI: assumes "∀x∈s. ¦x::real¦ ≤ B" shows "bounded s" unfolding bounded_def dist_real_def by (metis abs_minus_commute assms diff_0_right) lemma bounded_empty [simp]: "bounded {}" by (simp add: bounded_def) lemma bounded_subset: "bounded T ⟹ S ⊆ T ⟹ bounded S" by (metis bounded_def subset_eq) lemma bounded_interior[intro]: "bounded S ⟹ bounded(interior S)" by (metis bounded_subset interior_subset) lemma bounded_closure[intro]: assumes "bounded S" shows "bounded (closure S)" proof - from assms obtain x and a where a: "∀y∈S. dist x y ≤ a" unfolding bounded_def by auto { fix y assume "y ∈ closure S" then obtain f where f: "∀n. f n ∈ S" "(f ⤏ y) sequentially" unfolding closure_sequential by auto have "∀n. f n ∈ S ⟶ dist x (f n) ≤ a" using a by simp then have "eventually (λn. dist x (f n) ≤ a) sequentially" by (simp add: f(1)) have "dist x y ≤ a" apply (rule Lim_dist_ubound [of sequentially f]) apply (rule trivial_limit_sequentially) apply (rule f(2)) apply fact done } then show ?thesis unfolding bounded_def by auto qed lemma bounded_cball[simp,intro]: "bounded (cball x e)" apply (simp add: bounded_def) apply (rule_tac x=x in exI) apply (rule_tac x=e in exI) apply auto done lemma bounded_ball[simp,intro]: "bounded (ball x e)" by (metis ball_subset_cball bounded_cball bounded_subset) lemma bounded_Un[simp]: "bounded (S ∪ T) ⟷ bounded S ∧ bounded T" apply (auto simp add: bounded_def) by (metis Un_iff add_le_cancel_left dist_triangle le_max_iff_disj max.order_iff) lemma bounded_Union[intro]: "finite F ⟹ ∀S∈F. bounded S ⟹ bounded (⋃F)" by (induct rule: finite_induct[of F]) auto lemma bounded_UN [intro]: "finite A ⟹ ∀x∈A. bounded (B x) ⟹ bounded (⋃x∈A. B x)" by (induct set: finite) auto lemma bounded_insert [simp]: "bounded (insert x S) ⟷ bounded S" proof - have "∀y∈{x}. dist x y ≤ 0" by simp then have "bounded {x}" unfolding bounded_def by fast then show ?thesis by (metis insert_is_Un bounded_Un) qed lemma finite_imp_bounded [intro]: "finite S ⟹ bounded S" by (induct set: finite) simp_all lemma bounded_pos: "bounded S ⟷ (∃b>0. ∀x∈ S. norm x ≤ b)" apply (simp add: bounded_iff) apply (subgoal_tac "⋀x (y::real). 0 < 1 + ¦y¦ ∧ (x ≤ y ⟶ x ≤ 1 + ¦y¦)") apply metis apply arith done lemma bounded_pos_less: "bounded S ⟷ (∃b>0. ∀x∈ S. norm x < b)" apply (simp add: bounded_pos) apply (safe; rule_tac x="b+1" in exI; force) done lemma Bseq_eq_bounded: fixes f :: "nat ⇒ 'a::real_normed_vector" shows "Bseq f ⟷ bounded (range f)" unfolding Bseq_def bounded_pos by auto lemma bounded_Int[intro]: "bounded S ∨ bounded T ⟹ bounded (S ∩ T)" by (metis Int_lower1 Int_lower2 bounded_subset) lemma bounded_diff[intro]: "bounded S ⟹ bounded (S - T)" by (metis Diff_subset bounded_subset) lemma not_bounded_UNIV[simp, intro]: "¬ bounded (UNIV :: 'a::{real_normed_vector, perfect_space} set)" proof (auto simp add: bounded_pos not_le) obtain x :: 'a where "x ≠ 0" using perfect_choose_dist [OF zero_less_one] by fast fix b :: real assume b: "b >0" have b1: "b +1 ≥ 0" using b by simp with ‹x ≠ 0› have "b < norm (scaleR (b + 1) (sgn x))" by (simp add: norm_sgn) then show "∃x::'a. b < norm x" .. qed corollary cobounded_imp_unbounded: fixes S :: "'a::{real_normed_vector, perfect_space} set" shows "bounded (- S) ⟹ ~ (bounded S)" using bounded_Un [of S "-S"] by (simp add: sup_compl_top) lemma bounded_linear_image: assumes "bounded S" and "bounded_linear f" shows "bounded (f ` S)" proof - from assms(1) obtain b where b: "b > 0" "∀x∈S. norm x ≤ b" unfolding bounded_pos by auto from assms(2) obtain B where B: "B > 0" "∀x. norm (f x) ≤ B * norm x" using bounded_linear.pos_bounded by (auto simp add: ac_simps) { fix x assume "x ∈ S" then have "norm x ≤ b" using b by auto then have "norm (f x) ≤ B * b" using B(2) apply (erule_tac x=x in allE) apply (metis B(1) B(2) order_trans mult_le_cancel_left_pos) done } then show ?thesis unfolding bounded_pos apply (rule_tac x="b*B" in exI) using b B by (auto simp add: mult.commute) qed lemma bounded_scaling: fixes S :: "'a::real_normed_vector set" shows "bounded S ⟹ bounded ((λx. c *⇩_{R}x) ` S)" apply (rule bounded_linear_image) apply assumption apply (rule bounded_linear_scaleR_right) done lemma bounded_translation: fixes S :: "'a::real_normed_vector set" assumes "bounded S" shows "bounded ((λx. a + x) ` S)" proof - from assms obtain b where b: "b > 0" "∀x∈S. norm x ≤ b" unfolding bounded_pos by auto { fix x assume "x ∈ S" then have "norm (a + x) ≤ b + norm a" using norm_triangle_ineq[of a x] b by auto } then show ?thesis unfolding bounded_pos using norm_ge_zero[of a] b(1) and add_strict_increasing[of b 0 "norm a"] by (auto intro!: exI[of _ "b + norm a"]) qed lemma bounded_uminus [simp]: fixes X :: "'a::euclidean_space set" shows "bounded (uminus ` X) ⟷ bounded X" by (auto simp: bounded_def dist_norm; rule_tac x="-x" in exI; force simp add: add.commute norm_minus_commute) text‹Some theorems on sups and infs using the notion "bounded".› lemma bounded_real: "bounded (S::real set) ⟷ (∃a. ∀x∈S. ¦x¦ ≤ a)" by (simp add: bounded_iff) lemma bounded_imp_bdd_above: "bounded S ⟹ bdd_above (S :: real set)" by (auto simp: bounded_def bdd_above_def dist_real_def) (metis abs_le_D1 abs_minus_commute diff_le_eq) lemma bounded_imp_bdd_below: "bounded S ⟹ bdd_below (S :: real set)" by (auto simp: bounded_def bdd_below_def dist_real_def) (metis abs_le_D1 add.commute diff_le_eq) lemma bounded_inner_imp_bdd_above: assumes "bounded s" shows "bdd_above ((λx. x ∙ a) ` s)" by (simp add: assms bounded_imp_bdd_above bounded_linear_image bounded_linear_inner_left) lemma bounded_inner_imp_bdd_below: assumes "bounded s" shows "bdd_below ((λx. x ∙ a) ` s)" by (simp add: assms bounded_imp_bdd_below bounded_linear_image bounded_linear_inner_left) lemma bounded_has_Sup: fixes S :: "real set" assumes "bounded S" and "S ≠ {}" shows "∀x∈S. x ≤ Sup S" and "∀b. (∀x∈S. x ≤ b) ⟶ Sup S ≤ b" proof show "∀b. (∀x∈S. x ≤ b) ⟶ Sup S ≤ b" using assms by (metis cSup_least) qed (metis cSup_upper assms(1) bounded_imp_bdd_above) lemma Sup_insert: fixes S :: "real set" shows "bounded S ⟹ Sup (insert x S) = (if S = {} then x else max x (Sup S))" by (auto simp: bounded_imp_bdd_above sup_max cSup_insert_If) lemma Sup_insert_finite: fixes S :: "'a::conditionally_complete_linorder set" shows "finite S ⟹ Sup (insert x S) = (if S = {} then x else max x (Sup S))" by (simp add: cSup_insert sup_max) lemma bounded_has_Inf: fixes S :: "real set" assumes "bounded S" and "S ≠ {}" shows "∀x∈S. x ≥ Inf S" and "∀b. (∀x∈S. x ≥ b) ⟶ Inf S ≥ b" proof show "∀b. (∀x∈S. x ≥ b) ⟶ Inf S ≥ b" using assms by (metis cInf_greatest) qed (metis cInf_lower assms(1) bounded_imp_bdd_below) lemma Inf_insert: fixes S :: "real set" shows "bounded S ⟹ Inf (insert x S) = (if S = {} then x else min x (Inf S))" by (auto simp: bounded_imp_bdd_below inf_min cInf_insert_If) lemma Inf_insert_finite: fixes S :: "'a::conditionally_complete_linorder set" shows "finite S ⟹ Inf (insert x S) = (if S = {} then x else min x (Inf S))" by (simp add: cInf_eq_Min) lemma finite_imp_less_Inf: fixes a :: "'a::conditionally_complete_linorder" shows "⟦finite X; x ∈ X; ⋀x. x∈X ⟹ a < x⟧ ⟹ a < Inf X" by (induction X rule: finite_induct) (simp_all add: cInf_eq_Min Inf_insert_finite) lemma finite_less_Inf_iff: fixes a :: "'a :: conditionally_complete_linorder" shows "⟦finite X; X ≠ {}⟧ ⟹ a < Inf X ⟷ (∀x ∈ X. a < x)" by (auto simp: cInf_eq_Min) lemma finite_imp_Sup_less: fixes a :: "'a::conditionally_complete_linorder" shows "⟦finite X; x ∈ X; ⋀x. x∈X ⟹ a > x⟧ ⟹ a > Sup X" by (induction X rule: finite_induct) (simp_all add: cSup_eq_Max Sup_insert_finite) lemma finite_Sup_less_iff: fixes a :: "'a :: conditionally_complete_linorder" shows "⟦finite X; X ≠ {}⟧ ⟹ a > Sup X ⟷ (∀x ∈ X. a > x)" by (auto simp: cSup_eq_Max) subsection ‹Compactness› subsubsection ‹Bolzano-Weierstrass property› lemma heine_borel_imp_bolzano_weierstrass: assumes "compact s" and "infinite t" and "t ⊆ s" shows "∃x ∈ s. x islimpt t" proof (rule ccontr) assume "¬ (∃x ∈ s. x islimpt t)" then obtain f where f: "∀x∈s. x ∈ f x ∧ open (f x) ∧ (∀y∈t. y ∈ f x ⟶ y = x)" unfolding islimpt_def using bchoice[of s "λ x T. x ∈ T ∧ open T ∧ (∀y∈t. y ∈ T ⟶ y = x)"] by auto obtain g where g: "g ⊆ {t. ∃x. x ∈ s ∧ t = f x}" "finite g" "s ⊆ ⋃g" using assms(1)[unfolded compact_eq_heine_borel, THEN spec[where x="{t. ∃x. x∈s ∧ t = f x}"]] using f by auto from g(1,3) have g':"∀x∈g. ∃xa ∈ s. x = f xa" by auto { fix x y assume "x ∈ t" "y ∈ t" "f x = f y" then have "x ∈ f x" "y ∈ f x ⟶ y = x" using f[THEN bspec[where x=x]] and ‹t ⊆ s› by auto then have "x = y" using ‹f x = f y› and f[THEN bspec[where x=y]] and ‹y ∈ t› and ‹t ⊆ s› by auto } then have "inj_on f t" unfolding inj_on_def by simp then have "infinite (f ` t)" using assms(2) using finite_imageD by auto moreover { fix x assume "x ∈ t" "f x ∉ g" from g(3) assms(3) ‹x ∈ t› obtain h where "h ∈ g" and "x ∈ h" by auto then obtain y where "y ∈ s" "h = f y" using g'[THEN bspec[where x=h]] by auto then have "y = x" using f[THEN bspec[where x=y]] and ‹x∈t› and ‹x∈h›[unfolded ‹h = f y›] by auto then have False using ‹f x ∉ g› ‹h ∈ g› unfolding ‹h = f y› by auto } then have "f ` t ⊆ g" by auto ultimately show False using g(2) using finite_subset by auto qed lemma acc_point_range_imp_convergent_subsequence: fixes l :: "'a :: first_countable_topology" assumes l: "∀U. l∈U ⟶ open U ⟶ infinite (U ∩ range f)" shows "∃r. subseq r ∧ (f ∘ r) ⇢ l" proof - from countable_basis_at_decseq[of l] obtain A where A: "⋀i. open (A i)" "⋀i. l ∈ A i" "⋀S. open S ⟹ l ∈ S ⟹ eventually (λi. A i ⊆ S) sequentially" by blast def s ≡ "λn i. SOME j. i < j ∧ f j ∈ A (Suc n)" { fix n i have "infinite (A (Suc n) ∩ range f - f`{.. i})" using l A by auto then have "∃x. x ∈ A (Suc n) ∩ range f - f`{.. i}" unfolding ex_in_conv by (intro notI) simp then have "∃j. f j ∈ A (Suc n) ∧ j ∉ {.. i}" by auto then have "∃a. i < a ∧ f a ∈ A (Suc n)" by (auto simp: not_le) then have "i < s n i" "f (s n i) ∈ A (Suc n)" unfolding s_def by (auto intro: someI2_ex) } note s = this def r ≡ "rec_nat (s 0 0) s" have "subseq r" by (auto simp: r_def s subseq_Suc_iff) moreover have "(λn. f (r n)) ⇢ l" proof (rule topological_tendstoI) fix S assume "open S" "l ∈ S" with A(3) have "eventually (λi. A i ⊆ S) sequentially" by auto moreover { fix i assume "Suc 0 ≤ i" then have "f (r i) ∈ A i" by (cases i) (simp_all add: r_def s) } then have "eventually (λi. f (r i) ∈ A i) sequentially" by (auto simp: eventually_sequentially) ultimately show "eventually (λi. f (r i) ∈ S) sequentially" by eventually_elim auto qed ultimately show "∃r. subseq r ∧ (f ∘ r) ⇢ l" by (auto simp: convergent_def comp_def) qed lemma sequence_infinite_lemma: fixes f :: "nat ⇒ 'a::t1_space" assumes "∀n. f n ≠ l" and "(f ⤏ l) sequentially" shows "infinite (range f)" proof assume "finite (range f)" then have "closed (range f)" by (rule finite_imp_closed) then have "open (- range f)" by (rule open_Compl) from assms(1) have "l ∈ - range f" by auto from assms(2) have "eventually (λn. f n ∈ - range f) sequentially" using ‹open (- range f)› ‹l ∈ - range f› by (rule topological_tendstoD) then show False unfolding eventually_sequentially by auto qed lemma closure_insert: fixes x :: "'a::t1_space" shows "closure (insert x s) = insert x (closure s)" apply (rule closure_unique) apply (rule insert_mono [OF closure_subset]) apply (rule closed_insert [OF closed_closure]) apply (simp add: closure_minimal) done lemma islimpt_insert: fixes x :: "'a::t1_space" shows "x islimpt (insert a s) ⟷ x islimpt s" proof assume *: "x islimpt (insert a s)" show "x islimpt s" proof (rule islimptI) fix t assume t: "x ∈ t" "open t" show "∃y∈s. y ∈ t ∧ y ≠ x" proof (cases "x = a") case True obtain y where "y ∈ insert a s" "y ∈ t" "y ≠ x" using * t by (rule islimptE) with ‹x = a› show ?thesis by auto next case False with t have t': "x ∈ t - {a}" "open (t - {a})" by (simp_all add: open_Diff) obtain y where "y ∈ insert a s" "y ∈ t - {a}" "y ≠ x" using * t' by (rule islimptE) then show ?thesis by auto qed qed next assume "x islimpt s" then show "x islimpt (insert a s)" by (rule islimpt_subset) auto qed lemma islimpt_finite: fixes x :: "'a::t1_space" shows "finite s ⟹ ¬ x islimpt s" by (induct set: finite) (simp_all add: islimpt_insert) lemma islimpt_union_finite: fixes x :: "'a::t1_space" shows "finite s ⟹ x islimpt (s ∪ t) ⟷ x islimpt t" by (simp add: islimpt_Un islimpt_finite) lemma islimpt_eq_acc_point: fixes l :: "'a :: t1_space" shows "l islimpt S ⟷ (∀U. l∈U ⟶ open U ⟶ infinite (U ∩ S))" proof (safe intro!: islimptI) fix U assume "l islimpt S" "l ∈ U" "open U" "finite (U ∩ S)" then have "l islimpt S" "l ∈ (U - (U ∩ S - {l}))" "open (U - (U ∩ S - {l}))" by (auto intro: finite_imp_closed) then show False by (rule islimptE) auto next fix T assume *: "∀U. l∈U ⟶ open U ⟶ infinite (U ∩ S)" "l ∈ T" "open T" then have "infinite (T ∩ S - {l})" by auto then have "∃x. x ∈ (T ∩ S - {l})" unfolding ex_in_conv by (intro notI) simp then show "∃y∈S. y ∈ T ∧ y ≠ l" by auto qed lemma islimpt_range_imp_convergent_subsequence: fixes l :: "'a :: {t1_space, first_countable_topology}" assumes l: "l islimpt (range f)" shows "∃r. subseq r ∧ (f ∘ r) ⇢ l" using l unfolding islimpt_eq_acc_point by (rule acc_point_range_imp_convergent_subsequence) lemma sequence_unique_limpt: fixes f :: "nat ⇒ 'a::t2_space" assumes "(f ⤏ l) sequentially" and "l' islimpt (range f)" shows "l' = l" proof (rule ccontr) assume "l' ≠ l" obtain s t where "open s" "open t" "l' ∈ s" "l ∈ t" "s ∩ t = {}" using hausdorff [OF ‹l' ≠ l›] by auto have "eventually (λn. f n ∈ t) sequentially" using assms(1) ‹open t› ‹l ∈ t› by (rule topological_tendstoD) then obtain N where "∀n≥N. f n ∈ t" unfolding eventually_sequentially by auto have "UNIV = {..<N} ∪ {N..}" by auto then have "l' islimpt (f ` ({..<N} ∪ {N..}))" using assms(2) by simp then have "l' islimpt (f ` {..<N} ∪ f ` {N..})" by (simp add: image_Un) then have "l' islimpt (f ` {N..})" by (simp add: islimpt_union_finite) then obtain y where "y ∈ f ` {N..}" "y ∈ s" "y ≠ l'" using ‹l' ∈ s› ‹open s› by (rule islimptE) then obtain n where "N ≤ n" "f n ∈ s" "f n ≠ l'" by auto with ‹∀n≥N. f n ∈ t› have "f n ∈ s ∩ t" by simp with ‹s ∩ t = {}› show False by simp qed lemma bolzano_weierstrass_imp_closed: fixes s :: "'a::{first_countable_topology,t2_space} set" assumes "∀t. infinite t ∧ t ⊆ s --> (∃x ∈ s. x islimpt t)" shows "closed s" proof - { fix x l assume as: "∀n::nat. x n ∈ s" "(x ⤏ l) sequentially" then have "l ∈ s" proof (cases "∀n. x n ≠ l") case False then show "l∈s" using as(1) by auto next case True note cas = this with as(2) have "infinite (range x)" using sequence_infinite_lemma[of x l] by auto then obtain l' where "l'∈s" "l' islimpt (range x)" using assms[THEN spec[where x="range x"]] as(1) by auto then show "l∈s" using sequence_unique_limpt[of x l l'] using as cas by auto qed } then show ?thesis unfolding closed_sequential_limits by fast qed lemma compact_imp_bounded: assumes "compact U" shows "bounded U" proof - have "compact U" "∀x∈U. open (ball x 1)" "U ⊆ (⋃x∈U. ball x 1)" using assms by auto then obtain D where D: "D ⊆ U" "finite D" "U ⊆ (⋃x∈D. ball x 1)" by (rule compactE_image) from ‹finite D› have "bounded (⋃x∈D. ball x 1)" by (simp add: bounded_UN) then show "bounded U" using ‹U ⊆ (⋃x∈D. ball x 1)› by (rule bounded_subset) qed text‹In particular, some common special cases.› lemma compact_union [intro]: assumes "compact s" and "compact t" shows " compact (s ∪ t)" proof (rule compactI) fix f assume *: "Ball f open" "s ∪ t ⊆ ⋃f" from * ‹compact s› obtain s' where "s' ⊆ f ∧ finite s' ∧ s ⊆ ⋃s'" unfolding compact_eq_heine_borel by (auto elim!: allE[of _ f]) moreover from * ‹compact t› obtain t' where "t' ⊆ f ∧ finite t' ∧ t ⊆ ⋃t'" unfolding compact_eq_heine_borel by (auto elim!: allE[of _ f]) ultimately show "∃f'⊆f. finite f' ∧ s ∪ t ⊆ ⋃f'" by (auto intro!: exI[of _ "s' ∪ t'"]) qed lemma compact_Union [intro]: "finite S ⟹ (⋀T. T ∈ S ⟹ compact T) ⟹ compact (⋃S)" by (induct set: finite) auto lemma compact_UN [intro]: "finite A ⟹ (⋀x. x ∈ A ⟹ compact (B x)) ⟹ compact (⋃x∈A. B x)" unfolding SUP_def by (rule compact_Union) auto lemma closed_inter_compact [intro]: assumes "closed s" and "compact t" shows "compact (s ∩ t)" using compact_inter_closed [of t s] assms by (simp add: Int_commute) lemma compact_inter [intro]: fixes s t :: "'a :: t2_space set" assumes "compact s" and "compact t" shows "compact (s ∩ t)" using assms by (intro compact_inter_closed compact_imp_closed) lemma compact_sing [simp]: "compact {a}" unfolding compact_eq_heine_borel by auto lemma compact_insert [simp]: assumes "compact s" shows "compact (insert x s)" proof - have "compact ({x} ∪ s)" using compact_sing assms by (rule compact_union) then show ?thesis by simp qed lemma finite_imp_compact: "finite s ⟹ compact s" by (induct set: finite) simp_all lemma open_delete: fixes s :: "'a::t1_space set" shows "open s ⟹ open (s - {x})" by (simp add: open_Diff) text‹Compactness expressed with filters› lemma closure_iff_nhds_not_empty: "x ∈ closure X ⟷ (∀A. ∀S⊆A. open S ⟶ x ∈ S ⟶ X ∩ A ≠ {})" proof safe assume x: "x ∈ closure X" fix S A assume "open S" "x ∈ S" "X ∩ A = {}" "S ⊆ A" then have "x ∉ closure (-S)" by (auto simp: closure_complement subset_eq[symmetric] intro: interiorI) with x have "x ∈ closure X - closure (-S)" by auto also have "… ⊆ closure (X ∩ S)" using ‹open S› open_inter_closure_subset[of S X] by (simp add: closed_Compl ac_simps) finally have "X ∩ S ≠ {}" by auto then show False using ‹X ∩ A = {}› ‹S ⊆ A› by auto next assume "∀A S. S ⊆ A ⟶ open S ⟶ x ∈ S ⟶ X ∩ A ≠ {}" from this[THEN spec, of "- X", THEN spec, of "- closure X"] show "x ∈ closure X" by (simp add: closure_subset open_Compl) qed lemma compact_filter: "compact U ⟷ (∀F. F ≠ bot ⟶ eventually (λx. x ∈ U) F ⟶ (∃x∈U. inf (nhds x) F ≠ bot))" proof (intro allI iffI impI compact_fip[THEN iffD2] notI) fix F assume "compact U" assume F: "F ≠ bot" "eventually (λx. x ∈ U) F" then have "U ≠ {}" by (auto simp: eventually_False) def Z ≡ "closure ` {A. eventually (λx. x ∈ A) F}" then have "∀z∈Z. closed z" by auto moreover have ev_Z: "⋀z. z ∈ Z ⟹ eventually (λx. x ∈ z) F" unfolding Z_def by (auto elim: eventually_mono intro: set_mp[OF closure_subset]) have "(∀B ⊆ Z. finite B ⟶ U ∩ ⋂B ≠ {})" proof (intro allI impI) fix B assume "finite B" "B ⊆ Z" with ‹finite B› ev_Z F(2) have "eventually (λx. x ∈ U ∩ (⋂B)) F" by (auto simp: eventually_ball_finite_distrib eventually_conj_iff) with F show "U ∩ ⋂B ≠ {}" by (intro notI) (simp add: eventually_False) qed ultimately have "U ∩ ⋂Z ≠ {}" using ‹compact U› unfolding compact_fip by blast then obtain x where "x ∈ U" and x: "⋀z. z ∈ Z ⟹ x ∈ z" by auto have "⋀P. eventually P (inf (nhds x) F) ⟹ P ≠ bot" unfolding eventually_inf eventually_nhds proof safe fix P Q R S assume "eventually R F" "open S" "x ∈ S" with open_inter_closure_eq_empty[of S "{x. R x}"] x[of "closure {x. R x}"] have "S ∩ {x. R x} ≠ {}" by (auto simp: Z_def) moreover assume "Ball S Q" "∀x. Q x ∧ R x ⟶ bot x" ultimately show False by (auto simp: set_eq_iff) qed with ‹x ∈ U› show "∃x∈U. inf (nhds x) F ≠ bot" by (metis eventually_bot) next fix A assume A: "∀a∈A. closed a" "∀B⊆A. finite B ⟶ U ∩ ⋂B ≠ {}" "U ∩ ⋂A = {}" def F ≡ "INF a:insert U A. principal a" have "F ≠ bot" unfolding F_def proof (rule INF_filter_not_bot) fix X assume "X ⊆ insert U A" "finite X" moreover with A(2)[THEN spec, of "X - {U}"] have "U ∩ ⋂(X - {U}) ≠ {}" by auto ultimately show "(INF a:X. principal a) ≠ bot" by (auto simp add: INF_principal_finite principal_eq_bot_iff) qed moreover have "F ≤ principal U" unfolding F_def by auto then have "eventually (λx. x ∈ U) F" by (auto simp: le_filter_def eventually_principal) moreover assume "∀F. F ≠ bot ⟶ eventually (λx. x ∈ U) F ⟶ (∃x∈U. inf (nhds x) F ≠ bot)" ultimately obtain x where "x ∈ U" and x: "inf (nhds x) F ≠ bot" by auto { fix V assume "V ∈ A" then have "F ≤ principal V" unfolding F_def by (intro INF_lower2[of V]) auto then have V: "eventually (λx. x ∈ V) F" by (auto simp: le_filter_def eventually_principal) have "x ∈ closure V" unfolding closure_iff_nhds_not_empty proof (intro impI allI) fix S A assume "open S" "x ∈ S" "S ⊆ A" then have "eventually (λx. x ∈ A) (nhds x)" by (auto simp: eventually_nhds) with V have "eventually (λx. x ∈ V ∩ A) (inf (nhds x) F)" by (auto simp: eventually_inf) with x show "V ∩ A ≠ {}" by (auto simp del: Int_iff simp add: trivial_limit_def) qed then have "x ∈ V" using ‹V ∈ A› A(1) by simp } with ‹x∈U› have "x ∈ U ∩ ⋂A" by auto with ‹U ∩ ⋂A = {}› show False by auto qed definition "countably_compact U ⟷ (∀A. countable A ⟶ (∀a∈A. open a) ⟶ U ⊆ ⋃A ⟶ (∃T⊆A. finite T ∧ U ⊆ ⋃T))" lemma countably_compactE: assumes "countably_compact s" and "∀t∈C. open t" and "s ⊆ ⋃C" "countable C" obtains C' where "C' ⊆ C" and "finite C'" and "s ⊆ ⋃C'" using assms unfolding countably_compact_def by metis lemma countably_compactI: assumes "⋀C. ∀t∈C. open t ⟹ s ⊆ ⋃C ⟹ countable C ⟹ (∃C'⊆C. finite C' ∧ s ⊆ ⋃C')" shows "countably_compact s" using assms unfolding countably_compact_def by metis lemma compact_imp_countably_compact: "compact U ⟹ countably_compact U" by (auto simp: compact_eq_heine_borel countably_compact_def) lemma countably_compact_imp_compact: assumes "countably_compact U" and ccover: "countable B" "∀b∈B. open b" and basis: "⋀T x. open T ⟹ x ∈ T ⟹ x ∈ U ⟹ ∃b∈B. x ∈ b ∧ b ∩ U ⊆ T" shows "compact U" using ‹countably_compact U› unfolding compact_eq_heine_borel countably_compact_def proof safe fix A assume A: "∀a∈A. open a" "U ⊆ ⋃A" assume *: "∀A. countable A ⟶ (∀a∈A. open a) ⟶ U ⊆ ⋃A ⟶ (∃T⊆A. finite T ∧ U ⊆ ⋃T)" moreover def C ≡ "{b∈B. ∃a∈A. b ∩ U ⊆ a}" ultimately have "countable C" "∀a∈C. open a" unfolding C_def using ccover by auto moreover have "⋃A ∩ U ⊆ ⋃C" proof safe fix x a assume "x ∈ U" "x ∈ a" "a ∈ A" with basis[of a x] A obtain b where "b ∈ B" "x ∈ b" "b ∩ U ⊆ a" by blast with ‹a ∈ A› show "x ∈ ⋃C" unfolding C_def by auto qed then have "U ⊆ ⋃C" using ‹U ⊆ ⋃A› by auto ultimately obtain T where T: "T⊆C" "finite T" "U ⊆ ⋃T" using * by metis then have "∀t∈T. ∃a∈A. t ∩ U ⊆ a" by (auto simp: C_def) then obtain f where "∀t∈T. f t ∈ A ∧ t ∩ U ⊆ f t" unfolding bchoice_iff Bex_def .. with T show "∃T⊆A. finite T ∧ U ⊆ ⋃T" unfolding C_def by (intro exI[of _ "f`T"]) fastforce qed lemma countably_compact_imp_compact_second_countable: "countably_compact U ⟹ compact (U :: 'a :: second_countable_topology set)" proof (rule countably_compact_imp_compact) fix T and x :: 'a assume "open T" "x ∈ T" from topological_basisE[OF is_basis this] obtain b where "b ∈ (SOME B. countable B ∧ topological_basis B)" "x ∈ b" "b ⊆ T" . then show "∃b∈SOME B. countable B ∧ topological_basis B. x ∈ b ∧ b ∩ U ⊆ T" by blast qed (insert countable_basis topological_basis_open[OF is_basis], auto) lemma countably_compact_eq_compact: "countably_compact U ⟷ compact (U :: 'a :: second_countable_topology set)" using countably_compact_imp_compact_second_countable compact_imp_countably_compact by blast subsubsection‹Sequential compactness› definition seq_compact :: "'a::topological_space set ⇒ bool" where "seq_compact S ⟷ (∀f. (∀n. f n ∈ S) ⟶ (∃l∈S. ∃r. subseq r ∧ ((f ∘ r) ⤏ l) sequentially))" lemma seq_compactI: assumes "⋀f. ∀n. f n ∈ S ⟹ ∃l∈S. ∃r. subseq r ∧ ((f ∘ r) ⤏ l) sequentially" shows "seq_compact S" unfolding seq_compact_def using assms by fast lemma seq_compactE: assumes "seq_compact S" "∀n. f n ∈ S" obtains l r where "l ∈ S" "subseq r" "((f ∘ r) ⤏ l) sequentially" using assms unfolding seq_compact_def by fast lemma closed_sequentially: (* TODO: move upwards *) assumes "closed s" and "∀n. f n ∈ s" and "f ⇢ l" shows "l ∈ s" proof (rule ccontr) assume "l ∉ s" with ‹closed s› and ‹f ⇢ l› have "eventually (λn. f n ∈ - s) sequentially" by (fast intro: topological_tendstoD) with ‹∀n. f n ∈ s› show "False" by simp qed lemma seq_compact_inter_closed: assumes "seq_compact s" and "closed t" shows "seq_compact (s ∩ t)" proof (rule seq_compactI) fix f assume "∀n::nat. f n ∈ s ∩ t" hence "∀n. f n ∈ s" and "∀n. f n ∈ t" by simp_all from ‹seq_compact s› and ‹∀n. f n ∈ s› obtain l r where "l ∈ s" and r: "subseq r" and l: "(f ∘ r) ⇢ l" by (rule seq_compactE) from ‹∀n. f n ∈ t› have "∀n. (f ∘ r) n ∈ t" by simp from ‹closed t› and this and l have "l ∈ t" by (rule closed_sequentially) with ‹l ∈ s› and r and l show "∃l∈s ∩ t. ∃r. subseq r ∧ (f ∘ r) ⇢ l" by fast qed lemma seq_compact_closed_subset: assumes "closed s" and "s ⊆ t" and "seq_compact t" shows "seq_compact s" using assms seq_compact_inter_closed [of t s] by (simp add: Int_absorb1) lemma seq_compact_imp_countably_compact: fixes U :: "'a :: first_countable_topology set" assumes "seq_compact U" shows "countably_compact U" proof (safe intro!: countably_compactI) fix A assume A: "∀a∈A. open a" "U ⊆ ⋃A" "countable A" have subseq: "⋀X. range X ⊆ U ⟹ ∃r x. x ∈ U ∧ subseq r ∧ (X ∘ r) ⇢ x" using ‹seq_compact U› by (fastforce simp: seq_compact_def subset_eq) show "∃T⊆A. finite T ∧ U ⊆ ⋃T" proof cases assume "finite A" with A show ?thesis by auto next assume "infinite A" then have "A ≠ {}" by auto show ?thesis proof (rule ccontr) assume "¬ (∃T⊆A. finite T ∧ U ⊆ ⋃T)" then have "∀T. ∃x. T ⊆ A ∧ finite T ⟶ (x ∈ U - ⋃T)" by auto then obtain X' where T: "⋀T. T ⊆ A ⟹ finite T ⟹ X' T ∈ U - ⋃T" by metis def X ≡ "λn. X' (from_nat_into A ` {.. n})" have X: "⋀n. X n ∈ U - (⋃i≤n. from_nat_into A i)" using ‹A ≠ {}› unfolding X_def SUP_def by (intro T) (auto intro: from_nat_into) then have "range X ⊆ U" by auto with subseq[of X] obtain r x where "x ∈ U" and r: "subseq r" "(X ∘ r) ⇢ x" by auto from ‹x∈U› ‹U ⊆ ⋃A› from_nat_into_surj[OF ‹countable A›] obtain n where "x ∈ from_nat_into A n" by auto with r(2) A(1) from_nat_into[OF ‹A ≠ {}›, of n] have "eventually (λi. X (r i) ∈ from_nat_into A n) sequentially" unfolding tendsto_def by (auto simp: comp_def) then obtain N where "⋀i. N ≤ i ⟹ X (r i) ∈ from_nat_into A n" by (auto simp: eventually_sequentially) moreover from X have "⋀i. n ≤ r i ⟹ X (r i) ∉ from_nat_into A n" by auto moreover from ‹subseq r›[THEN seq_suble, of "max n N"] have "∃i. n ≤ r i ∧ N ≤ i" by (auto intro!: exI[of _ "max n N"]) ultimately show False by auto qed qed qed lemma compact_imp_seq_compact: fixes U :: "'a :: first_countable_topology set" assumes "compact U" shows "seq_compact U" unfolding seq_compact_def proof safe fix X :: "nat ⇒ 'a" assume "∀n. X n ∈ U" then have "eventually (λx. x ∈ U) (filtermap X sequentially)" by (auto simp: eventually_filtermap) moreover have "filtermap X sequentially ≠ bot" by (simp add: trivial_limit_def eventually_filtermap) ultimately obtain x where "x ∈ U" and x: "inf (nhds x) (filtermap X sequentially) ≠ bot" (is "?F ≠ _") using ‹compact U› by (auto simp: compact_filter) from countable_basis_at_decseq[of x] obtain A where A: "⋀i. open (A i)" "⋀i. x ∈ A i" "⋀S. open S ⟹ x ∈ S ⟹ eventually (λi. A i ⊆ S) sequentially" by blast def s ≡ "λn i. SOME j. i < j ∧ X j ∈ A (Suc n)" { fix n i have "∃a. i < a ∧ X a ∈ A (Suc n)" proof (rule ccontr) assume "¬ (∃a>i. X a ∈ A (Suc n))" then have "⋀a. Suc i ≤ a ⟹ X a ∉ A (Suc n)" by auto then have "eventually (λx. x ∉ A (Suc n)) (filtermap X sequentially)" by (auto simp: eventually_filtermap eventually_sequentially) moreover have "eventually (λx. x ∈ A (Suc n)) (nhds x)" using A(1,2)[of "Suc n"] by (auto simp: eventually_nhds) ultimately have "eventually (λx. False) ?F" by (auto simp add: eventually_inf) with x show False by (simp add: eventually_False) qed then have "i < s n i" "X (s n i) ∈ A (Suc n)" unfolding s_def by (auto intro: someI2_ex) } note s = this def r ≡ "rec_nat (s 0 0) s" have "subseq r" by (auto simp: r_def s subseq_Suc_iff) moreover have "(λn. X (r n)) ⇢ x" proof (rule topological_tendstoI) fix S assume "open S" "x ∈ S" with A(3) have "eventually (λi. A i ⊆ S) sequentially" by auto moreover { fix i assume "Suc 0 ≤ i" then have "X (r i) ∈ A i" by (cases i) (simp_all add: r_def s) } then have "eventually (λi. X (r i) ∈ A i) sequentially" by (auto simp: eventually_sequentially) ultimately show "eventually (λi. X (r i) ∈ S) sequentially" by eventually_elim auto qed ultimately show "∃x ∈ U. ∃r. subseq r ∧ (X ∘ r) ⇢ x" using ‹x ∈ U› by (auto simp: convergent_def comp_def) qed lemma countably_compact_imp_acc_point: assumes "countably_compact s" and "countable t" and "infinite t" and "t ⊆ s" shows "∃x∈s. ∀U. x∈U ∧ open U ⟶ infinite (U ∩ t)" proof (rule ccontr) def C ≡ "(λF. interior (F ∪ (- t))) ` {F. finite F ∧ F ⊆ t }" note ‹countably_compact s› moreover have "∀t∈C. open t" by (auto simp: C_def) moreover assume "¬ (∃x∈s. ∀U. x∈U ∧ open U ⟶ infinite (U ∩ t))" then have s: "⋀x. x ∈ s ⟹ ∃U. x∈U ∧ open U ∧ finite (U ∩ t)" by metis have "s ⊆ ⋃C" using ‹t ⊆ s› unfolding C_def Union_image_eq apply (safe dest!: s) apply (rule_tac a="U ∩ t" in UN_I) apply (auto intro!: interiorI simp add: finite_subset) done moreover from ‹countable t› have "countable C" unfolding C_def by (auto intro: countable_Collect_finite_subset) ultimately obtain D where "D ⊆ C" "finite D" "s ⊆ ⋃D" by (rule countably_compactE) then obtain E where E: "E ⊆ {F. finite F ∧ F ⊆ t }" "finite E" and s: "s ⊆ (⋃F∈E. interior (F ∪ (- t)))" by (metis (lifting) Union_image_eq finite_subset_image C_def) from s ‹t ⊆ s› have "t ⊆ ⋃E" using interior_subset by blast moreover have "finite (⋃E)" using E by auto ultimately show False using ‹infinite t› by (auto simp: finite_subset) qed lemma countable_acc_point_imp_seq_compact: fixes s :: "'a::first_countable_topology set" assumes "∀t. infinite t ∧ countable t ∧ t ⊆ s ⟶ (∃x∈s. ∀U. x∈U ∧ open U ⟶ infinite (U ∩ t))" shows "seq_compact s" proof - { fix f :: "nat ⇒ 'a" assume f: "∀n. f n ∈ s" have "∃l∈s. ∃r. subseq r ∧ ((f ∘ r) ⤏ l) sequentially" proof (cases "finite (range f)") case True obtain l where "infinite {n. f n = f l}" using pigeonhole_infinite[OF _ True] by auto then obtain r where "subseq r" and fr: "∀n. f (r n) = f l" using infinite_enumerate by blast then have "subseq r ∧ (f ∘ r) ⇢ f l" by (simp add: fr o_def) with f show "∃l∈s. ∃r. subseq r ∧ (f ∘ r) ⇢ l" by auto next case False with f assms have "∃x∈s. ∀U. x∈U ∧ open U ⟶ infinite (U ∩ range f)" by auto then obtain l where "l ∈ s" "∀U. l∈U ∧ open U ⟶ infinite (U ∩ range f)" .. from this(2) have "∃r. subseq r ∧ ((f ∘ r) ⤏ l) sequentially" using acc_point_range_imp_convergent_subsequence[of l f] by auto with ‹l ∈ s› show "∃l∈s. ∃r. subseq r ∧ ((f ∘ r) ⤏ l) sequentially" .. qed } then show ?thesis unfolding seq_compact_def by auto qed lemma seq_compact_eq_countably_compact: fixes U :: "'a :: first_countable_topology set" shows "seq_compact U ⟷ countably_compact U" using countable_acc_point_imp_seq_compact countably_compact_imp_acc_point seq_compact_imp_countably_compact by metis lemma seq_compact_eq_acc_point: fixes s :: "'a :: first_countable_topology set" shows "seq_compact s ⟷ (∀t. infinite t ∧ countable t ∧ t ⊆ s --> (∃x∈s. ∀U. x∈U ∧ open U ⟶ infinite (U ∩ t)))" using countable_acc_point_imp_seq_compact[of s] countably_compact_imp_acc_point[of s] seq_compact_imp_countably_compact[of s] by metis lemma seq_compact_eq_compact: fixes U :: "'a :: second_countable_topology set" shows "seq_compact U ⟷ compact U" using seq_compact_eq_countably_compact countably_compact_eq_compact by blast lemma bolzano_weierstrass_imp_seq_compact: fixes s :: "'a::{t1_space, first_countable_topology} set" shows "∀t. infinite t ∧ t ⊆ s --> (∃x ∈ s. x islimpt t) ⟹ seq_compact s" by (rule countable_acc_point_imp_seq_compact) (metis islimpt_eq_acc_point) subsubsection‹Totally bounded› lemma cauchy_def: "Cauchy s ⟷ (∀e>0. ∃N. ∀m n. m ≥ N ∧ n ≥ N --> dist(s m)(s n) < e)" unfolding Cauchy_def by metis lemma seq_compact_imp_totally_bounded: assumes "seq_compact s" shows "∀e>0. ∃k. finite k ∧ k ⊆ s ∧ s ⊆ (⋃x∈k. ball x e)" proof - { fix e::real assume "e > 0" assume *: "⋀k. finite k ⟹ k ⊆ s ⟹ ¬ s ⊆ (⋃x∈k. ball x e)" let ?Q = "λx n r. r ∈ s ∧ (∀m < (n::nat). ¬ (dist (x m) r < e))" have "∃x. ∀n::nat. ?Q x n (x n)" proof (rule dependent_wellorder_choice) fix n x assume "⋀y. y < n ⟹ ?Q x y (x y)" then have "¬ s ⊆ (⋃x∈x ` {0..<n}. ball x e)" using *[of "x ` {0 ..< n}"] by (auto simp: subset_eq) then obtain z where z:"z∈s" "z ∉ (⋃x∈x ` {0..<n}. ball x e)" unfolding subset_eq by auto show "∃r. ?Q x n r" using z by auto qed simp then obtain x where "∀n::nat. x n ∈ s" and x:"⋀n m. m < n ⟹ ¬ (dist (x m) (x n) < e)" by blast then obtain l r where "l ∈ s" and r:"subseq r" and "((x ∘ r) ⤏ l) sequentially" using assms by (metis seq_compact_def) from this(3) have "Cauchy (x ∘ r)" using LIMSEQ_imp_Cauchy by auto then obtain N::nat where "⋀m n. N ≤ m ⟹ N ≤ n ⟹ dist ((x ∘ r) m) ((x ∘ r) n) < e" unfolding cauchy_def using ‹e > 0› by blast then have False using x[of "r N" "r (N+1)"] r by (auto simp: subseq_def) } then show ?thesis by metis qed subsubsection‹Heine-Borel theorem› lemma seq_compact_imp_heine_borel: fixes s :: "'a :: metric_space set" assumes "seq_compact s" shows "compact s" proof - from seq_compact_imp_totally_bounded[OF ‹seq_compact s›] obtain f where f: "∀e>0. finite (f e) ∧ f e ⊆ s ∧ s ⊆ (⋃x∈f e. ball x e)" unfolding choice_iff' .. def K ≡ "(λ(x, r). ball x r) ` ((⋃e ∈ ℚ ∩ {0 <..}. f e) × ℚ)" have "countably_compact s" using ‹seq_compact s› by (rule seq_compact_imp_countably_compact) then show "compact s" proof (rule countably_compact_imp_compact) show "countable K" unfolding K_def using f by (auto intro: countable_finite countable_subset countable_rat intro!: countable_image countable_SIGMA countable_UN) show "∀b∈K. open b" by (auto simp: K_def) next fix T x assume T: "open T" "x ∈ T" and x: "x ∈ s" from openE[OF T] obtain e where "0 < e" "ball x e ⊆ T" by auto then have "0 < e / 2" "ball x (e / 2) ⊆ T" by auto from Rats_dense_in_real[OF ‹0 < e / 2›] obtain r where "r ∈ ℚ" "0 < r" "r < e / 2" by auto from f[rule_format, of r] ‹0 < r› ‹x ∈ s› obtain k where "k ∈ f r" "x ∈ ball k r" unfolding Union_image_eq by auto from ‹r ∈ ℚ› ‹0 < r› ‹k ∈ f r› have "ball k r ∈ K" by (auto simp: K_def) then show "∃b∈K. x ∈ b ∧ b ∩ s ⊆ T" proof (rule bexI[rotated], safe) fix y assume "y ∈ ball k r" with ‹r < e / 2› ‹x ∈ ball k r› have "dist x y < e" by (intro dist_double[where x = k and d=e]) (auto simp: dist_commute) with ‹ball x e ⊆ T› show "y ∈ T" by auto next show "x ∈ ball k r" by fact qed qed qed lemma compact_eq_seq_compact_metric: "compact (s :: 'a::metric_space set) ⟷ seq_compact s" using compact_imp_seq_compact seq_compact_imp_heine_borel by blast lemma compact_def: "compact (S :: 'a::metric_space set) ⟷ (∀f. (∀n. f n ∈ S) ⟶ (∃l∈S. ∃r. subseq r ∧ (f ∘ r) ⇢ l))" unfolding compact_eq_seq_compact_metric seq_compact_def by auto subsubsection ‹Complete the chain of compactness variants› lemma compact_eq_bolzano_weierstrass: fixes s :: "'a::metric_space set" shows "compact s ⟷ (∀t. infinite t ∧ t ⊆ s --> (∃x ∈ s. x islimpt t))" (is "?lhs = ?rhs") proof assume ?lhs then show ?rhs using heine_borel_imp_bolzano_weierstrass[of s] by auto next assume ?rhs then show ?lhs unfolding compact_eq_seq_compact_metric by (rule bolzano_weierstrass_imp_seq_compact) qed lemma bolzano_weierstrass_imp_bounded: "∀t. infinite t ∧ t ⊆ s ⟶ (∃x ∈ s. x islimpt t) ⟹ bounded s" using compact_imp_bounded unfolding compact_eq_bolzano_weierstrass . subsection ‹Metric spaces with the Heine-Borel property› text ‹ A metric space (or topological vector space) is said to have the Heine-Borel property if every closed and bounded subset is compact. › class heine_borel = metric_space + assumes bounded_imp_convergent_subsequence: "bounded (range f) ⟹ ∃l r. subseq r ∧ ((f ∘ r) ⤏ l) sequentially" lemma bounded_closed_imp_seq_compact: fixes s::"'a::heine_borel set" assumes "bounded s" and "closed s" shows "seq_compact s" proof (unfold seq_compact_def, clarify) fix f :: "nat ⇒ 'a" assume f: "∀n. f n ∈ s" with ‹bounded s› have "bounded (range f)" by (auto intro: bounded_subset) obtain l r where r: "subseq r" and l: "((f ∘ r) ⤏ l) sequentially" using bounded_imp_convergent_subsequence [OF ‹bounded (range f)›] by auto from f have fr: "∀n. (f ∘ r) n ∈ s" by simp have "l ∈ s" using ‹closed s› fr l by (rule closed_sequentially) show "∃l∈s. ∃r. subseq r ∧ ((f ∘ r) ⤏ l) sequentially" using ‹l ∈ s› r l by blast qed lemma compact_eq_bounded_closed: fixes s :: "'a::heine_borel set" shows "compact s ⟷ bounded s ∧ closed s" (is "?lhs = ?rhs") proof assume ?lhs then show ?rhs using compact_imp_closed compact_imp_bounded by blast next assume ?rhs then show ?lhs using bounded_closed_imp_seq_compact[of s] unfolding compact_eq_seq_compact_metric by auto qed lemma compact_components: fixes s :: "'a::heine_borel set" shows "⟦compact s; c ∈ components s⟧ ⟹ compact c" by (meson bounded_subset closed_components in_components_subset compact_eq_bounded_closed) (* TODO: is this lemma necessary? *) lemma bounded_increasing_convergent: fixes s :: "nat ⇒ real" shows "bounded {s n| n. True} ⟹ ∀n. s n ≤ s (Suc n) ⟹ ∃l. s ⇢ l" using Bseq_mono_convergent[of