Theory Extended_Nonnegative_Real

```(*  Title:      HOL/Library/Extended_Nonnegative_Real.thy
Author:     Johannes Hölzl
*)

section ‹The type of non-negative extended real numbers›

theory Extended_Nonnegative_Real
imports Extended_Real Indicator_Function
begin

assumes "b ≠ (-∞::ereal)" "a ≥ b"
shows "a = b + (a-b)"
by (metis add.commute assms ereal_eq_minus_iff ereal_minus_le_iff ereal_plus_eq_PInfty)

shows "F ≠ bot ⟹ Limsup F (λx. c + f x) = c + Limsup F f"
by (rule Limsup_compose_continuous_mono)

shows "F ≠ bot ⟹ Liminf F (λx. c + f x) = c + Liminf F f"
by (rule Liminf_compose_continuous_mono)

shows "F ≠ bot ⟹ Liminf F (λx. f x + c) = Liminf F f + c"
by (rule Liminf_compose_continuous_mono)

lemma sums_offset:
fixes f g :: "nat ⇒ 'a :: {t2_space, topological_comm_monoid_add}"
assumes "(λn. f (n + i)) sums l" shows "f sums (l + (∑j<i. f j))"
proof  -
have "(λk. (∑n<k. f (n + i)) + (∑j<i. f j)) ⇢ l + (∑j<i. f j)"
using assms by (auto intro!: tendsto_add simp: sums_def)
moreover
{ fix k :: nat
have "(∑j<k + i. f j) = (∑j=i..<k + i. f j) + (∑j=0..<i. f j)"
by (subst sum.union_disjoint[symmetric]) (auto intro!: sum.cong)
also have "(∑j=i..<k + i. f j) = (∑j∈(λn. n + i)`{0..<k}. f j)"
finally have "(∑j<k + i. f j) = (∑n<k. f (n + i)) + (∑j<i. f j)"
by (auto simp: inj_on_def atLeast0LessThan sum.reindex) }
ultimately have "(λk. (∑n<k + i. f n)) ⇢ l + (∑j<i. f j)"
by simp
then show ?thesis
unfolding sums_def by (rule LIMSEQ_offset)
qed

lemma suminf_offset:
fixes f g :: "nat ⇒ 'a :: {t2_space, topological_comm_monoid_add}"
shows "summable (λj. f (j + i)) ⟹ suminf f = (∑j. f (j + i)) + (∑j<i. f j)"
by (intro sums_unique[symmetric] sums_offset summable_sums)

lemma eventually_at_left_1: "(⋀z::real. 0 < z ⟹ z < 1 ⟹ P z) ⟹ eventually P (at_left 1)"
by (subst eventually_at_left[of 0]) (auto intro: exI[of _ 0])

lemma mult_eq_1:
fixes a b :: "'a :: {ordered_semiring, comm_monoid_mult}"
shows "0 ≤ a ⟹ a ≤ 1 ⟹ b ≤ 1 ⟹ a * b = 1 ⟷ (a = 1 ∧ b = 1)"
by (metis mult.left_neutral eq_iff mult.commute mult_right_mono)

fixes a b :: ereal
shows "¦b¦ ≠ ∞ ⟹ (a + b) - b = a"
by (cases a b rule: ereal2_cases) auto

shows "0 ≤ x ⟹ x + top = top"

shows "0 ≤ x ⟹ top + x = top"

lemma le_lfp: "mono f ⟹ x ≤ lfp f ⟹ f x ≤ lfp f"
by (subst lfp_unfold) (auto dest: monoD)

lemma lfp_transfer:
assumes α: "sup_continuous α" and f: "sup_continuous f" and mg: "mono g"
assumes bot: "α bot ≤ lfp g" and eq: "⋀x. x ≤ lfp f ⟹ α (f x) = g (α x)"
shows "α (lfp f) = lfp g"
proof (rule antisym)
note mf = sup_continuous_mono[OF f]
have f_le_lfp: "(f ^^ i) bot ≤ lfp f" for i
by (induction i) (auto intro: le_lfp mf)

have "α ((f ^^ i) bot) ≤ lfp g" for i
by (induction i) (auto simp: bot eq f_le_lfp intro!: le_lfp mg)
then show "α (lfp f) ≤ lfp g"
unfolding sup_continuous_lfp[OF f]
by (subst α[THEN sup_continuousD])
(auto intro!: mono_funpow sup_continuous_mono[OF f] SUP_least)

show "lfp g ≤ α (lfp f)"
by (rule lfp_lowerbound) (simp add: eq[symmetric] lfp_fixpoint[OF mf])
qed

lemma sup_continuous_applyD: "sup_continuous f ⟹ sup_continuous (λx. f x h)"
using sup_continuous_apply[THEN sup_continuous_compose] .

lemma sup_continuous_SUP[order_continuous_intros]:
fixes M :: "_ ⇒ _ ⇒ 'a::complete_lattice"
assumes M: "⋀i. i ∈ I ⟹ sup_continuous (M i)"
shows  "sup_continuous (SUP i∈I. M i)"
unfolding sup_continuous_def by (auto simp add: sup_continuousD [OF M] image_comp intro: SUP_commute)

lemma sup_continuous_apply_SUP[order_continuous_intros]:
fixes M :: "_ ⇒ _ ⇒ 'a::complete_lattice"
shows "(⋀i. i ∈ I ⟹ sup_continuous (M i)) ⟹ sup_continuous (λx. SUP i∈I. M i x)"
unfolding SUP_apply[symmetric] by (rule sup_continuous_SUP)

lemma sup_continuous_lfp'[order_continuous_intros]:
assumes 1: "sup_continuous f"
assumes 2: "⋀g. sup_continuous g ⟹ sup_continuous (f g)"
shows "sup_continuous (lfp f)"
proof -
have "sup_continuous ((f ^^ i) bot)" for i
proof (induction i)
case (Suc i) then show ?case
by (auto intro!: 2)
then show ?thesis
unfolding sup_continuous_lfp[OF 1] by (intro order_continuous_intros)
qed

lemma sup_continuous_lfp''[order_continuous_intros]:
assumes 1: "⋀s. sup_continuous (f s)"
assumes 2: "⋀g. sup_continuous g ⟹ sup_continuous (λs. f s (g s))"
shows "sup_continuous (λx. lfp (f x))"
proof -
have "sup_continuous (λx. (f x ^^ i) bot)" for i
proof (induction i)
case (Suc i) then show ?case
by (auto intro!: 2)
then show ?thesis
unfolding sup_continuous_lfp[OF 1] by (intro order_continuous_intros)
qed

lemma mono_INF_fun:
"(⋀x y. mono (F x y)) ⟹ mono (λz x. INF y ∈ X x. F x y z :: 'a :: complete_lattice)"
by (auto intro!: INF_mono[OF bexI] simp: le_fun_def mono_def)

lemma continuous_on_cmult_ereal:
"¦c::ereal¦ ≠ ∞ ⟹ continuous_on A f ⟹ continuous_on A (λx. c * f x)"
using tendsto_cmult_ereal[of c f "f x" "at x within A" for x]
by (auto simp: continuous_on_def simp del: tendsto_cmult_ereal)

lemma real_of_nat_Sup:
assumes "A ≠ {}" "bdd_above A"
shows "of_nat (Sup A) = (SUP a∈A. of_nat a :: real)"
proof (intro antisym)
show "(SUP a∈A. of_nat a::real) ≤ of_nat (Sup A)"
using assms by (intro cSUP_least of_nat_mono) (auto intro: cSup_upper)
have "Sup A ∈ A"
using assms by (auto simp: Sup_nat_def bdd_above_nat)
then show "of_nat (Sup A) ≤ (SUP a∈A. of_nat a::real)"
by (intro cSUP_upper bdd_above_image_mono assms) (auto simp: mono_def)
qed

lemma (in complete_lattice) SUP_sup_const1:
"I ≠ {} ⟹ (SUP i∈I. sup c (f i)) = sup c (SUP i∈I. f i)"
using SUP_sup_distrib[of "λ_. c" I f] by simp

lemma (in complete_lattice) SUP_sup_const2:
"I ≠ {} ⟹ (SUP i∈I. sup (f i) c) = sup (SUP i∈I. f i) c"
using SUP_sup_distrib[of f I "λ_. c"] by simp

lemma one_less_of_natD:
assumes "(1::'a::linordered_semidom) < of_nat n" shows "1 < n"
by (cases n) (use assms in auto)

subsection ‹Defining the extended non-negative reals›

text ‹Basic definitions and type class setup›

typedef ennreal = "{x :: ereal. 0 ≤ x}"
morphisms enn2ereal e2ennreal'
by auto

definition "e2ennreal x = e2ennreal' (max 0 x)"

lemma enn2ereal_range: "e2ennreal ` {0..} = UNIV"
proof -
have "∃y≥0. x = e2ennreal y" for x
by (cases x) (auto simp: e2ennreal_def max_absorb2)
then show ?thesis
by (auto simp: image_iff Bex_def)
qed

lemma type_definition_ennreal': "type_definition enn2ereal e2ennreal {x. 0 ≤ x}"
using type_definition_ennreal
by (auto simp: type_definition_def e2ennreal_def max_absorb2)

setup_lifting type_definition_ennreal'

declare [[coercion e2ennreal]]

instantiation ennreal :: complete_linorder
begin

lift_definition top_ennreal :: ennreal is top by (rule top_greatest)
lift_definition bot_ennreal :: ennreal is 0 by (rule order_refl)
lift_definition sup_ennreal :: "ennreal ⇒ ennreal ⇒ ennreal" is sup by (rule le_supI1)
lift_definition inf_ennreal :: "ennreal ⇒ ennreal ⇒ ennreal" is inf by (rule le_infI)

lift_definition Inf_ennreal :: "ennreal set ⇒ ennreal" is "Inf"
by (rule Inf_greatest)

lift_definition Sup_ennreal :: "ennreal set ⇒ ennreal" is "sup 0 ∘ Sup"
by auto

lift_definition less_eq_ennreal :: "ennreal ⇒ ennreal ⇒ bool" is "(≤)" .
lift_definition less_ennreal :: "ennreal ⇒ ennreal ⇒ bool" is "(<)" .

instance
by standard
(transfer ; auto simp: Inf_lower Inf_greatest Sup_upper Sup_least le_max_iff_disj max.absorb1)+

end

lemma pcr_ennreal_enn2ereal[simp]: "pcr_ennreal (enn2ereal x) x"

lemma rel_fun_eq_pcr_ennreal: "rel_fun (=) pcr_ennreal f g ⟷ f = enn2ereal ∘ g"
by (auto simp: rel_fun_def ennreal.pcr_cr_eq cr_ennreal_def)

instantiation ennreal :: infinity
begin

definition infinity_ennreal :: ennreal
where
[simp]: "∞ = (top::ennreal)"

instance ..

end

instantiation ennreal :: "{semiring_1_no_zero_divisors, comm_semiring_1}"
begin

lift_definition one_ennreal :: ennreal is 1 by simp
lift_definition zero_ennreal :: ennreal is 0 by simp
lift_definition plus_ennreal :: "ennreal ⇒ ennreal ⇒ ennreal" is "(+)" by simp
lift_definition times_ennreal :: "ennreal ⇒ ennreal ⇒ ennreal" is "(*)" by simp

instance
by standard (transfer; auto simp: field_simps ereal_right_distrib)+

end

instantiation ennreal :: minus
begin

lift_definition minus_ennreal :: "ennreal ⇒ ennreal ⇒ ennreal" is "λa b. max 0 (a - b)"
by simp

instance ..

end

instance ennreal :: numeral ..

instantiation ennreal :: inverse
begin

lift_definition inverse_ennreal :: "ennreal ⇒ ennreal" is inverse
by (rule inverse_ereal_ge0I)

definition divide_ennreal :: "ennreal ⇒ ennreal ⇒ ennreal"
where "x div y = x * inverse (y :: ennreal)"

instance ..

end

lemma ennreal_zero_less_one: "0 < (1::ennreal)" ― ‹TODO: remove›
by transfer auto

instance ennreal :: dioid
proof (standard; transfer)
fix a b :: ereal assume "0 ≤ a" "0 ≤ b" then show "(a ≤ b) = (∃c∈Collect ((≤) 0). b = a + c)"
unfolding ereal_ex_split Bex_def
by (cases a b rule: ereal2_cases) (auto intro!: exI[of _ "real_of_ereal (b - a)"])
qed

instance ennreal :: ordered_comm_semiring
by standard
(transfer ; auto intro: add_mono mult_mono mult_ac ereal_left_distrib ereal_mult_left_mono)+

instance ennreal :: linordered_nonzero_semiring
proof
fix a b::ennreal
show "a < b ⟹ a + 1 < b + 1"
qed (transfer; simp)

proof
fix a b c d :: ennreal show "a < b ⟹ c < d ⟹ a + c < b + d"
qed

declare [[coercion "of_nat :: nat ⇒ ennreal"]]

lemma e2ennreal_neg: "x ≤ 0 ⟹ e2ennreal x = 0"
unfolding zero_ennreal_def e2ennreal_def by (simp add: max_absorb1)

lemma e2ennreal_mono: "x ≤ y ⟹ e2ennreal x ≤ e2ennreal y"
by (cases "0 ≤ x" "0 ≤ y" rule: bool.exhaust[case_product bool.exhaust])
(auto simp: e2ennreal_neg less_eq_ennreal.abs_eq eq_onp_def)

lemma enn2ereal_nonneg[simp]: "0 ≤ enn2ereal x"
using ennreal.enn2ereal[of x] by simp

lemma ereal_ennreal_cases:
obtains b where "0 ≤ a" "a = enn2ereal b" | "a < 0"
using e2ennreal'_inverse[of a, symmetric] by (cases "0 ≤ a") (auto intro: enn2ereal_nonneg)

lemma rel_fun_liminf[transfer_rule]: "rel_fun (rel_fun (=) pcr_ennreal) pcr_ennreal liminf liminf"
proof -
have "rel_fun (rel_fun (=) pcr_ennreal) pcr_ennreal (λx. sup 0 (liminf x)) liminf"
unfolding liminf_SUP_INF[abs_def] by (transfer_prover_start, transfer_step+; simp)
then show ?thesis
apply (subst (asm) (2) rel_fun_def)
apply (subst (2) rel_fun_def)
apply (auto simp: comp_def max.absorb2 Liminf_bounded rel_fun_eq_pcr_ennreal)
done
qed

lemma rel_fun_limsup[transfer_rule]: "rel_fun (rel_fun (=) pcr_ennreal) pcr_ennreal limsup limsup"
proof -
have "rel_fun (rel_fun (=) pcr_ennreal) pcr_ennreal (λx. INF n. sup 0 (SUP i∈{n..}. x i)) limsup"
unfolding limsup_INF_SUP[abs_def] by (transfer_prover_start, transfer_step+; simp)
then show ?thesis
unfolding limsup_INF_SUP[abs_def]
apply (subst (asm) (2) rel_fun_def)
apply (subst (2) rel_fun_def)
apply (auto simp: comp_def max.absorb2 Sup_upper2 rel_fun_eq_pcr_ennreal)
apply (subst (asm) max.absorb2)
apply (auto intro: SUP_upper2)
done
qed

lemma sum_enn2ereal[simp]: "(⋀i. i ∈ I ⟹ 0 ≤ f i) ⟹ (∑i∈I. enn2ereal (f i)) = enn2ereal (sum f I)"
by (induction I rule: infinite_finite_induct) (auto simp: sum_nonneg zero_ennreal.rep_eq plus_ennreal.rep_eq)

lemma transfer_e2ennreal_sum [transfer_rule]:
"rel_fun (rel_fun (=) pcr_ennreal) (rel_fun (=) pcr_ennreal) sum sum"
by (auto intro!: rel_funI simp: rel_fun_eq_pcr_ennreal comp_def)

lemma enn2ereal_of_nat[simp]: "enn2ereal (of_nat n) = ereal n"
by (induction n) (auto simp: zero_ennreal.rep_eq one_ennreal.rep_eq plus_ennreal.rep_eq)

lemma enn2ereal_numeral[simp]: "enn2ereal (numeral a) = numeral a"
by (metis enn2ereal_of_nat numeral_eq_ereal of_nat_numeral)

lemma transfer_numeral[transfer_rule]: "pcr_ennreal (numeral a) (numeral a)"
unfolding cr_ennreal_def pcr_ennreal_def by auto

subsection ‹Cancellation simprocs›

lemma ennreal_add_left_cancel: "a + b = a + c ⟷ a = (∞::ennreal) ∨ b = c"

lemma ennreal_add_left_cancel_le: "a + b ≤ a + c ⟷ a = (∞::ennreal) ∨ b ≤ c"

fixes a b c :: ereal
shows "0 ≤ a ⟹ 0 ≤ b ⟹ a + b < a + c ⟷ a ≠ ∞ ∧ b < c"
by (cases a b c rule: ereal3_cases) auto

lemma ennreal_add_left_cancel_less: "a + b < a + c ⟷ a ≠ (∞::ennreal) ∧ b < c"
unfolding infinity_ennreal_def

ML ‹
structure Cancel_Ennreal_Common =
struct
(* copied from src/HOL/Tools/nat_numeral_simprocs.ML *)
fun find_first_t _    _ []         = raise TERM("find_first_t", [])
| find_first_t past u (t::terms) =
if u aconv t then (rev past @ terms)
else find_first_t (t::past) u terms

fun dest_summing (Const (\<^const_name>‹Groups.plus›, _) \$ t \$ u, ts) =
dest_summing (t, dest_summing (u, ts))
| dest_summing (t, ts) = t :: ts

val mk_sum = Arith_Data.long_mk_sum
fun dest_sum t = dest_summing (t, [])
val find_first = find_first_t []
val trans_tac = Numeral_Simprocs.trans_tac
val norm_ss =
simpset_of (put_simpset HOL_basic_ss \<^context>
fun norm_tac ctxt = ALLGOALS (simp_tac (put_simpset norm_ss ctxt))
fun simplify_meta_eq ctxt cancel_th th =
Arith_Data.simplify_meta_eq [] ctxt
([th, cancel_th] MRS trans)
fun mk_eq (a, b) = HOLogic.mk_Trueprop (HOLogic.mk_eq (a, b))
end

structure Eq_Ennreal_Cancel = ExtractCommonTermFun
(open Cancel_Ennreal_Common
val mk_bal = HOLogic.mk_eq
val dest_bal = HOLogic.dest_bin \<^const_name>‹HOL.eq› \<^typ>‹ennreal›
fun simp_conv _ _ = SOME @{thm ennreal_add_left_cancel}
)

structure Le_Ennreal_Cancel = ExtractCommonTermFun
(open Cancel_Ennreal_Common
val mk_bal = HOLogic.mk_binrel \<^const_name>‹Orderings.less_eq›
val dest_bal = HOLogic.dest_bin \<^const_name>‹Orderings.less_eq› \<^typ>‹ennreal›
fun simp_conv _ _ = SOME @{thm ennreal_add_left_cancel_le}
)

structure Less_Ennreal_Cancel = ExtractCommonTermFun
(open Cancel_Ennreal_Common
val mk_bal = HOLogic.mk_binrel \<^const_name>‹Orderings.less›
val dest_bal = HOLogic.dest_bin \<^const_name>‹Orderings.less› \<^typ>‹ennreal›
fun simp_conv _ _ = SOME @{thm ennreal_add_left_cancel_less}
)
›

simproc_setup ennreal_eq_cancel
("(l::ennreal) + m = n" | "(l::ennreal) = m + n") =
‹K (fn ctxt => fn ct => Eq_Ennreal_Cancel.proc ctxt (Thm.term_of ct))›

simproc_setup ennreal_le_cancel
("(l::ennreal) + m ≤ n" | "(l::ennreal) ≤ m + n") =
‹K (fn ctxt => fn ct => Le_Ennreal_Cancel.proc ctxt (Thm.term_of ct))›

simproc_setup ennreal_less_cancel
("(l::ennreal) + m < n" | "(l::ennreal) < m + n") =
‹K (fn ctxt => fn ct => Less_Ennreal_Cancel.proc ctxt (Thm.term_of ct))›

subsection ‹Order with top›

lemma ennreal_zero_less_top[simp]: "0 < (top::ennreal)"

lemma ennreal_one_less_top[simp]: "1 < (top::ennreal)"

lemma ennreal_zero_neq_top[simp]: "0 ≠ (top::ennreal)"

lemma ennreal_top_neq_zero[simp]: "(top::ennreal) ≠ 0"

lemma ennreal_top_neq_one[simp]: "top ≠ (1::ennreal)"
by transfer (simp add: top_ereal_def one_ereal_def flip: ereal_max)

lemma ennreal_one_neq_top[simp]: "1 ≠ (top::ennreal)"
by transfer (simp add: top_ereal_def one_ereal_def flip: ereal_max)

fixes a b :: ennreal
shows "a + b < top ⟷ a < top ∧ b < top"
by transfer (auto simp: top_ereal_def)

fixes a b :: ennreal
shows "a + b = top ⟷ a = top ∨ b = top"
by transfer (auto simp: top_ereal_def)

lemma ennreal_sum_less_top[simp]:
fixes f :: "'a ⇒ ennreal"
shows "finite I ⟹ (∑i∈I. f i) < top ⟷ (∀i∈I. f i < top)"
by (induction I rule: finite_induct) auto

lemma ennreal_sum_eq_top[simp]:
fixes f :: "'a ⇒ ennreal"
shows "finite I ⟹ (∑i∈I. f i) = top ⟷ (∃i∈I. f i = top)"
by (induction I rule: finite_induct) auto

lemma ennreal_mult_eq_top_iff:
fixes a b :: ennreal
shows "a * b = top ⟷ (a = top ∧ b ≠ 0) ∨ (b = top ∧ a ≠ 0)"
by transfer (auto simp: top_ereal_def)

lemma ennreal_top_eq_mult_iff:
fixes a b :: ennreal
shows "top = a * b ⟷ (a = top ∧ b ≠ 0) ∨ (b = top ∧ a ≠ 0)"
using ennreal_mult_eq_top_iff[of a b] by auto

lemma ennreal_mult_less_top:
fixes a b :: ennreal
shows "a * b < top ⟷ (a = 0 ∨ b = 0 ∨ (a < top ∧ b < top))"
by transfer (auto simp add: top_ereal_def)

lemma top_power_ennreal: "top ^ n = (if n = 0 then 1 else top :: ennreal)"
by (induction n) (simp_all add: ennreal_mult_eq_top_iff)

lemma ennreal_prod_eq_0[simp]:
fixes f :: "'a ⇒ ennreal"
shows "(prod f A = 0) = (finite A ∧ (∃i∈A. f i = 0))"
by (induction A rule: infinite_finite_induct) auto

lemma ennreal_prod_eq_top:
fixes f :: "'a ⇒ ennreal"
shows "(∏i∈I. f i) = top ⟷ (finite I ∧ ((∀i∈I. f i ≠ 0) ∧ (∃i∈I. f i = top)))"
by (induction I rule: infinite_finite_induct) (auto simp: ennreal_mult_eq_top_iff)

lemma ennreal_top_mult: "top * a = (if a = 0 then 0 else top :: ennreal)"

lemma ennreal_mult_top: "a * top = (if a = 0 then 0 else top :: ennreal)"

lemma enn2ereal_eq_top_iff[simp]: "enn2ereal x = ∞ ⟷ x = top"

lemma enn2ereal_top[simp]: "enn2ereal top = ∞"

lemma e2ennreal_infty[simp]: "e2ennreal ∞ = top"

lemma ennreal_top_minus[simp]: "top - x = (top::ennreal)"
by transfer (auto simp: top_ereal_def max_def)

lemma minus_top_ennreal: "x - top = (if x = top then top else 0:: ennreal)"
by transfer (use ereal_eq_minus_iff top_ereal_def in force)

lemma bot_ennreal: "bot = (0::ennreal)"
by transfer rule

lemma ennreal_of_nat_neq_top[simp]: "of_nat i ≠ (top::ennreal)"
by (induction i) auto

lemma numeral_eq_of_nat: "(numeral a::ennreal) = of_nat (numeral a)"
by simp

lemma of_nat_less_top: "of_nat i < (top::ennreal)"
using less_le_trans[of "of_nat i" "of_nat (Suc i)" "top::ennreal"]
by simp

lemma top_neq_numeral[simp]: "top ≠ (numeral i::ennreal)"
using of_nat_less_top[of "numeral i"] by simp

lemma ennreal_numeral_less_top[simp]: "numeral i < (top::ennreal)"
using of_nat_less_top[of "numeral i"] by simp

lemma ennreal_add_bot[simp]: "bot + x = (x::ennreal)"
by transfer simp

lemma add_top_right_ennreal [simp]: "x + top = (top :: ennreal)"
by (cases x) auto

lemma add_top_left_ennreal [simp]: "top + x = (top :: ennreal)"
by (cases x) auto

lemma ennreal_top_mult_left [simp]: "x ≠ 0 ⟹ x * top = (top :: ennreal)"
by (subst ennreal_mult_eq_top_iff) auto

lemma ennreal_top_mult_right [simp]: "x ≠ 0 ⟹ top * x = (top :: ennreal)"
by (subst ennreal_mult_eq_top_iff) auto

lemma power_top_ennreal [simp]: "n > 0 ⟹ top ^ n = (top :: ennreal)"
by (induction n) auto

lemma power_eq_top_ennreal_iff: "x ^ n = top ⟷ x = (top :: ennreal) ∧ n > 0"
by (induction n) (auto simp: ennreal_mult_eq_top_iff)

lemma ennreal_mult_le_mult_iff: "c ≠ 0 ⟹ c ≠ top ⟹ c * a ≤ c * b ⟷ a ≤ (b :: ennreal)"
including ennreal.lifting
by (transfer, subst ereal_mult_le_mult_iff) (auto simp: top_ereal_def)

lemma power_mono_ennreal: "x ≤ y ⟹ x ^ n ≤ (y ^ n :: ennreal)"
by (induction n) (auto intro!: mult_mono)

instance ennreal :: semiring_char_0
proof (standard, safe intro!: linorder_injI)
have *: "1 + of_nat k ≠ (0::ennreal)" for k
using add_pos_nonneg[OF zero_less_one, of "of_nat k :: ennreal"] by auto
fix x y :: nat assume "x < y" "of_nat x = (of_nat y::ennreal)" then show False
qed

subsection ‹Arithmetic›

lemma ennreal_minus_zero[simp]: "a - (0::ennreal) = a"
by transfer (auto simp: max_def)

fixes x y z :: ennreal shows "y ≠ top ⟹ (x + y) - y = x"
by transfer (metis ereal_eq_minus_iff max_absorb2 not_MInfty_nonneg top_ereal_def)

fixes x y z :: ennreal shows "y ≠ top ⟹ (y + x) - y = x"

lemma
fixes a b :: ennreal
shows "a - b = 0 ⟹ a ≤ b"
by transfer (metis ereal_diff_gr0 le_cases max.absorb2 not_less)

lemma ennreal_minus_cancel:
fixes a b c :: ennreal
shows "c ≠ top ⟹ a ≤ c ⟹ b ≤ c ⟹ c - a = c - b ⟹ a = b"

fixes a b c :: "ennreal"
shows "sup (c + a) (c + b) = c + sup a b"
by transfer (metis add_left_mono le_cases sup.absorb2 sup.orderE)

fixes a b c :: ennreal
shows "a ≤ b ⟹ c + b - a = c + (b - a)"

lemma mult_divide_eq_ennreal:
fixes a b :: ennreal
shows "b ≠ 0 ⟹ b ≠ top ⟹ (a * b) / b = a"
unfolding divide_ennreal_def
apply transfer
by (metis abs_ereal_ge0 divide_ereal_def ereal_divide_eq ereal_times_divide_eq top_ereal_def)

lemma divide_mult_eq: "a ≠ 0 ⟹ a ≠ ∞ ⟹ x * a / (b * a) = x / (b::ennreal)"
unfolding divide_ennreal_def infinity_ennreal_def
apply transfer
subgoal for a b c
apply (cases a b c rule: ereal3_cases)
apply (auto simp: top_ereal_def)
done
done

lemma ennreal_mult_divide_eq:
fixes a b :: ennreal
shows "b ≠ 0 ⟹ b ≠ top ⟹ (a * b) / b = a"
by (fact mult_divide_eq_ennreal)

fixes a b :: ennreal
shows "b ≠ ∞ ⟹ (a + b) - b = a"
by simp

lemma ennreal_minus_eq_0:
"a - b = 0 ⟹ a ≤ (b::ennreal)"
by transfer (metis ereal_diff_gr0 le_cases max.absorb2 not_less)

lemma ennreal_mono_minus_cancel:
fixes a b c :: ennreal
shows "a - b ≤ a - c ⟹ a < top ⟹ b ≤ a ⟹ c ≤ a ⟹ c ≤ b"
by transfer
(auto simp add: max.absorb2 ereal_diff_positive top_ereal_def dest: ereal_mono_minus_cancel)

lemma ennreal_mono_minus:
fixes a b c :: ennreal
shows "c ≤ b ⟹ a - b ≤ a - c"
by transfer (meson ereal_minus_mono max.mono order_refl)

lemma ennreal_minus_pos_iff:
fixes a b :: ennreal
shows "a < top ∨ b < top ⟹ 0 < a - b ⟹ b < a"
by transfer (use add.left_neutral ereal_minus_le_iff less_irrefl not_less in fastforce)

lemma ennreal_inverse_top[simp]: "inverse top = (0::ennreal)"
by transfer (simp add: top_ereal_def ereal_inverse_eq_0)

lemma ennreal_inverse_zero[simp]: "inverse 0 = (top::ennreal)"
by transfer (simp add: top_ereal_def ereal_inverse_eq_0)

lemma ennreal_top_divide: "top / (x::ennreal) = (if x = top then 0 else top)"
unfolding divide_ennreal_def
by transfer (simp add: top_ereal_def ereal_inverse_eq_0 ereal_0_gt_inverse)

lemma ennreal_zero_divide[simp]: "0 / (x::ennreal) = 0"

lemma ennreal_divide_zero[simp]: "x / (0::ennreal) = (if x = 0 then 0 else top)"

lemma ennreal_divide_top[simp]: "x / (top::ennreal) = 0"

lemma ennreal_times_divide: "a * (b / c) = a * b / (c::ennreal)"
unfolding divide_ennreal_def
by transfer (simp add: divide_ereal_def[symmetric] ereal_times_divide_eq)

lemma ennreal_zero_less_divide: "0 < a / b ⟷ (0 < a ∧ b < (top::ennreal))"
unfolding divide_ennreal_def
by transfer (auto simp: ereal_zero_less_0_iff top_ereal_def ereal_0_gt_inverse)

lemma add_divide_distrib_ennreal: "(a + b) / c = a / c + b / (c :: ennreal)"

lemma divide_right_mono_ennreal:
fixes a b c :: ennreal
shows "a ≤ b ⟹ a / c ≤ b / c"
unfolding divide_ennreal_def by (intro mult_mono) auto

lemma ennreal_mult_strict_right_mono: "(a::ennreal) < c ⟹ 0 < b ⟹ b < top ⟹ a * b < c * b"
by transfer (auto intro!: ereal_mult_strict_right_mono)

lemma ennreal_indicator_less[simp]:
"indicator A x ≤ (indicator B x::ennreal) ⟷ (x ∈ A ⟶ x ∈ B)"

lemma ennreal_inverse_positive: "0 < inverse x ⟷ (x::ennreal) ≠ top"
by transfer (simp add: ereal_0_gt_inverse top_ereal_def)

lemma ennreal_inverse_mult': "((0 < b ∨ a < top) ∧ (0 < a ∨ b < top)) ⟹ inverse (a * b::ennreal) = inverse a * inverse b"
apply transfer
subgoal for a b
by (cases a b rule: ereal2_cases) (auto simp: top_ereal_def)
done

lemma ennreal_inverse_mult: "a < top ⟹ b < top ⟹ inverse (a * b::ennreal) = inverse a * inverse b"
apply transfer
subgoal for a b
by (cases a b rule: ereal2_cases) (auto simp: top_ereal_def)
done

lemma ennreal_inverse_1[simp]: "inverse (1::ennreal) = 1"
by transfer simp

lemma ennreal_inverse_eq_0_iff[simp]: "inverse (a::ennreal) = 0 ⟷ a = top"
by transfer (simp add: ereal_inverse_eq_0 top_ereal_def)

lemma ennreal_inverse_eq_top_iff[simp]: "inverse (a::ennreal) = top ⟷ a = 0"

lemma ennreal_divide_eq_0_iff[simp]: "(a::ennreal) / b = 0 ⟷ (a = 0 ∨ b = top)"

lemma ennreal_divide_eq_top_iff: "(a::ennreal) / b = top ⟷ ((a ≠ 0 ∧ b = 0) ∨ (a = top ∧ b ≠ top))"
by (auto simp add: divide_ennreal_def ennreal_mult_eq_top_iff)

lemma one_divide_one_divide_ennreal[simp]: "1 / (1 / c) = (c::ennreal)"
including ennreal.lifting
unfolding divide_ennreal_def
by transfer auto

lemma ennreal_mult_left_cong:
"((a::ennreal) ≠ 0 ⟹ b = c) ⟹ a * b = a * c"
by (cases "a = 0") simp_all

lemma ennreal_mult_right_cong:
"((a::ennreal) ≠ 0 ⟹ b = c) ⟹ b * a = c * a"
by (cases "a = 0") simp_all

lemma ennreal_zero_less_mult_iff: "0 < a * b ⟷ 0 < a ∧ 0 < (b::ennreal)"
by transfer (auto simp add: ereal_zero_less_0_iff le_less)

lemma less_diff_eq_ennreal:
fixes a b c :: ennreal
shows "b < top ∨ c < top ⟹ a < b - c ⟷ a + c < b"
apply transfer
subgoal for a b c
by (cases a b c rule: ereal3_cases) (auto split: split_max)
done

fixes a b :: ennreal shows "a ≤ b ⟹ b - a + a = b"
unfolding infinity_ennreal_def

lemma ennreal_diff_self[simp]: "a ≠ top ⟹ a - a = (0::ennreal)"

lemma ennreal_minus_mono:
fixes a b c :: ennreal
shows "a ≤ c ⟹ d ≤ b ⟹ a - b ≤ c - d"
by transfer (meson ereal_minus_mono max.mono order_refl)

lemma ennreal_minus_eq_top[simp]: "a - (b::ennreal) = top ⟷ a = top"

lemma ennreal_divide_self[simp]: "a ≠ 0 ⟹ a < top ⟹ a / a = (1::ennreal)"
by (metis mult_1 mult_divide_eq_ennreal top.not_eq_extremum)

subsection ‹Coercion from \<^typ>‹real› to \<^typ>‹ennreal››

lift_definition ennreal :: "real ⇒ ennreal" is "sup 0 ∘ ereal"
by simp

declare [[coercion ennreal]]

lemma ennreal_cong: "x = y ⟹ ennreal x = ennreal y"
by simp

lemma ennreal_cases[cases type: ennreal]:
fixes x :: ennreal
obtains (real) r :: real where "0 ≤ r" "x = ennreal r" | (top) "x = top"
apply transfer
subgoal for x thesis
by (cases x) (auto simp: max.absorb2 top_ereal_def)
done

lemmas ennreal2_cases = ennreal_cases[case_product ennreal_cases]
lemmas ennreal3_cases = ennreal_cases[case_product ennreal2_cases]

lemma ennreal_neq_top[simp]: "ennreal r ≠ top"
by transfer (simp add: top_ereal_def zero_ereal_def flip: ereal_max)

lemma top_neq_ennreal[simp]: "top ≠ ennreal r"
using ennreal_neq_top[of r] by (auto simp del: ennreal_neq_top)

lemma ennreal_less_top[simp]: "ennreal x < top"
by transfer (simp add: top_ereal_def max_def)

lemma ennreal_neg: "x ≤ 0 ⟹ ennreal x = 0"

lemma ennreal_inj[simp]:
"0 ≤ a ⟹ 0 ≤ b ⟹ ennreal a = ennreal b ⟷ a = b"
by (transfer fixing: a b) (auto simp: max_absorb2)

lemma ennreal_le_iff[simp]: "0 ≤ y ⟹ ennreal x ≤ ennreal y ⟷ x ≤ y"
by (auto simp: ennreal_def zero_ereal_def less_eq_ennreal.abs_eq eq_onp_def split: split_max)

lemma le_ennreal_iff: "0 ≤ r ⟹ x ≤ ennreal r ⟷ (∃q≥0. x = ennreal q ∧ q ≤ r)"
by (cases x) (auto simp: top_unique)

lemma ennreal_less_iff: "0 ≤ r ⟹ ennreal r < ennreal q ⟷ r < q"
unfolding not_le[symmetric] by auto

lemma ennreal_eq_zero_iff[simp]: "0 ≤ x ⟹ ennreal x = 0 ⟷ x = 0"
by transfer (auto simp: max_absorb2)

lemma ennreal_less_zero_iff[simp]: "0 < ennreal x ⟷ 0 < x"
by transfer (auto simp: max_def)

lemma ennreal_lessI: "0 < q ⟹ r < q ⟹ ennreal r < ennreal q"
by (cases "0 ≤ r") (auto simp: ennreal_less_iff ennreal_neg)

lemma ennreal_leI: "x ≤ y ⟹ ennreal x ≤ ennreal y"
by (cases "0 ≤ y") (auto simp: ennreal_neg)

lemma enn2ereal_ennreal[simp]: "0 ≤ x ⟹ enn2ereal (ennreal x) = x"

lemma e2ennreal_enn2ereal[simp]: "e2ennreal (enn2ereal x) = x"
by (simp add: e2ennreal_def max_absorb2 ennreal.enn2ereal_inverse)

lemma enn2ereal_e2ennreal: "x ≥ 0 ⟹ enn2ereal (e2ennreal x) = x"
by (metis e2ennreal_enn2ereal ereal_ennreal_cases not_le)

lemma e2ennreal_ereal [simp]: "e2ennreal (ereal x) = ennreal x"
by (metis e2ennreal_def enn2ereal_inverse ennreal.rep_eq sup_ereal_def)

lemma ennreal_0[simp]: "ennreal 0 = 0"
by (simp add: ennreal_def max.absorb1 zero_ennreal.abs_eq)

lemma ennreal_1[simp]: "ennreal 1 = 1"

lemma ennreal_eq_0_iff: "ennreal x = 0 ⟷ x ≤ 0"
by (cases "0 ≤ x") (auto simp: ennreal_neg)

lemma ennreal_le_iff2: "ennreal x ≤ ennreal y ⟷ ((0 ≤ y ∧ x ≤ y) ∨ (x ≤ 0 ∧ y ≤ 0))"
by (cases "0 ≤ y") (auto simp: ennreal_eq_0_iff ennreal_neg)

lemma ennreal_eq_1[simp]: "ennreal x = 1 ⟷ x = 1"
by (cases "0 ≤ x") (auto simp: ennreal_neg simp flip: ennreal_1)

lemma ennreal_le_1[simp]: "ennreal x ≤ 1 ⟷ x ≤ 1"
by (cases "0 ≤ x") (auto simp: ennreal_neg simp flip: ennreal_1)

lemma ennreal_ge_1[simp]: "ennreal x ≥ 1 ⟷ x ≥ 1"
by (cases "0 ≤ x") (auto simp: ennreal_neg simp flip: ennreal_1)

lemma one_less_ennreal[simp]: "1 < ennreal x ⟷ 1 < x"
by (meson ennreal_le_1 linorder_not_le)

lemma ennreal_plus[simp]:
"0 ≤ a ⟹ 0 ≤ b ⟹ ennreal (a + b) = ennreal a + ennreal b"
by (transfer fixing: a b) (auto simp: max_absorb2)

lemma add_mono_ennreal: "x < ennreal y ⟹ x' < ennreal y' ⟹ x + x' < ennreal (y + y')"
by (metis (full_types) add_strict_mono ennreal_less_zero_iff ennreal_plus less_le not_less zero_le)

lemma sum_ennreal[simp]: "(⋀i. i ∈ I ⟹ 0 ≤ f i) ⟹ (∑i∈I. ennreal (f i)) = ennreal (sum f I)"
by (induction I rule: infinite_finite_induct) (auto simp: sum_nonneg)

lemma sum_list_ennreal[simp]:
assumes "⋀x. x ∈ set xs ⟹ f x ≥ 0"
shows   "sum_list (map (λx. ennreal (f x)) xs) = ennreal (sum_list (map f xs))"
using assms
proof (induction xs)
case (Cons x xs)
from Cons have "(∑x←x # xs. ennreal (f x)) = ennreal (f x) + ennreal (sum_list (map f xs))"
by simp
also from Cons.prems have "… = ennreal (f x + sum_list (map f xs))"
by (intro ennreal_plus [symmetric] sum_list_nonneg) auto
finally show ?case by simp
qed simp_all

lemma ennreal_of_nat_eq_real_of_nat: "of_nat i = ennreal (of_nat i)"
by (induction i) simp_all

lemma of_nat_le_ennreal_iff[simp]: "0 ≤ r ⟹ of_nat i ≤ ennreal r ⟷ of_nat i ≤ r"

lemma ennreal_le_of_nat_iff[simp]: "ennreal r ≤ of_nat i ⟷ r ≤ of_nat i"

lemma ennreal_indicator: "ennreal (indicator A x) = indicator A x"
by (auto split: split_indicator)

lemma ennreal_numeral[simp]: "ennreal (numeral n) = numeral n"
using ennreal_of_nat_eq_real_of_nat[of "numeral n"] by simp

lemma ennreal_less_numeral_iff [simp]: "ennreal n < numeral w ⟷ n < numeral w"
by (metis ennreal_less_iff ennreal_numeral less_le not_less zero_less_numeral)

lemma numeral_less_ennreal_iff [simp]: "numeral w < ennreal n ⟷ numeral w < n"
using ennreal_less_iff zero_le_numeral by fastforce

lemma numeral_le_ennreal_iff [simp]: "numeral n ≤ ennreal m ⟷ numeral n ≤ m"
by (metis not_le ennreal_less_numeral_iff)

lemma min_ennreal: "0 ≤ x ⟹ 0 ≤ y ⟹ min (ennreal x) (ennreal y) = ennreal (min x y)"
by (auto split: split_min)

lemma ennreal_half[simp]: "ennreal (1/2) = inverse 2"

lemma ennreal_minus: "0 ≤ q ⟹ ennreal r - ennreal q = ennreal (r - q)"
by transfer
(simp add: max.absorb2 zero_ereal_def flip: ereal_max)

lemma ennreal_minus_top[simp]: "ennreal a - top = 0"

lemma e2eenreal_enn2ereal_diff [simp]:
"e2ennreal(enn2ereal x - enn2ereal y) = x - y" for x y
by (cases x, cases y, auto simp add: ennreal_minus e2ennreal_neg)

lemma ennreal_mult: "0 ≤ a ⟹ 0 ≤ b ⟹ ennreal (a * b) = ennreal a * ennreal b"

lemma ennreal_mult': "0 ≤ a ⟹ ennreal (a * b) = ennreal a * ennreal b"
by (cases "0 ≤ b") (auto simp: ennreal_mult ennreal_neg mult_nonneg_nonpos)

lemma indicator_mult_ennreal: "indicator A x * ennreal r = ennreal (indicator A x * r)"
by (simp split: split_indicator)

lemma ennreal_mult'': "0 ≤ b ⟹ ennreal (a * b) = ennreal a * ennreal b"
by (cases "0 ≤ a") (auto simp: ennreal_mult ennreal_neg mult_nonpos_nonneg)

lemma numeral_mult_ennreal: "0 ≤ x ⟹ numeral b * ennreal x = ennreal (numeral b * x)"

lemma ennreal_power: "0 ≤ r ⟹ ennreal r ^ n = ennreal (r ^ n)"
by (induction n) (auto simp: ennreal_mult)

lemma power_eq_top_ennreal: "x ^ n = top ⟷ (n ≠ 0 ∧ (x::ennreal) = top)"
by (cases x rule: ennreal_cases)
(auto simp: ennreal_power top_power_ennreal)

lemma inverse_ennreal: "0 < r ⟹ inverse (ennreal r) = ennreal (inverse r)"

lemma divide_ennreal: "0 ≤ r ⟹ 0 < q ⟹ ennreal r / ennreal q = ennreal (r / q)"
by (simp add: divide_ennreal_def inverse_ennreal ennreal_mult[symmetric] inverse_eq_divide)

lemma ennreal_inverse_power: "inverse (x ^ n :: ennreal) = inverse x ^ n"
proof (cases x rule: ennreal_cases)
case top with power_eq_top_ennreal[of x n] show ?thesis
by (cases "n = 0") auto
next
case (real r) then show ?thesis
proof (cases "x = 0")
case False then show ?thesis
by (smt (verit, best) ennreal_0 ennreal_power inverse_ennreal
inverse_nonnegative_iff_nonnegative power_inverse real zero_less_power)
qed

lemma power_divide_distrib_ennreal [algebra_simps]:
"(x / y) ^ n = x ^ n / (y ^ n :: ennreal)"
by (simp add: divide_ennreal_def algebra_simps ennreal_inverse_power)

lemma ennreal_divide_numeral: "0 ≤ x ⟹ ennreal x / numeral b = ennreal (x / numeral b)"
by (subst divide_ennreal[symmetric]) auto

lemma prod_ennreal: "(⋀i. i ∈ A ⟹ 0 ≤ f i) ⟹ (∏i∈A. ennreal (f i)) = ennreal (prod f A)"
by (induction A rule: infinite_finite_induct)
(auto simp: ennreal_mult prod_nonneg)

lemma prod_mono_ennreal:
assumes "⋀x. x ∈ A ⟹ f x ≤ (g x :: ennreal)"
shows   "prod f A ≤ prod g A"
using assms by (induction A rule: infinite_finite_induct) (auto intro!: mult_mono)

lemma mult_right_ennreal_cancel: "a * ennreal c = b * ennreal c ⟷ (a = b ∨ c ≤ 0)"
proof (cases "0 ≤ c")
case True
then show ?thesis
by (metis ennreal_eq_0_iff ennreal_mult_right_cong ennreal_neq_top mult_divide_eq_ennreal)
qed (use ennreal_neg in auto)

lemma ennreal_le_epsilon:
"(⋀e::real. y < top ⟹ 0 < e ⟹ x ≤ y + ennreal e) ⟹ x ≤ y"
apply (cases y rule: ennreal_cases)
apply (cases x rule: ennreal_cases)
apply (auto simp flip: ennreal_plus simp add: top_unique intro: zero_less_one field_le_epsilon)
done

lemma ennreal_rat_dense:
fixes x y :: ennreal
shows "x < y ⟹ ∃r::rat. x < real_of_rat r ∧ real_of_rat r < y"
proof transfer
fix x y :: ereal assume xy: "0 ≤ x" "0 ≤ y" "x < y"
moreover
from ereal_dense3[OF ‹x < y›]
obtain r where r: "x < ereal (real_of_rat r)" "ereal (real_of_rat r) < y"
by auto
then have "0 ≤ r"
using le_less_trans[OF ‹0 ≤ x› ‹x < ereal (real_of_rat r)›] by auto
with r show "∃r. x < (sup 0 ∘ ereal) (real_of_rat r) ∧ (sup 0 ∘ ereal) (real_of_rat r) < y"
by (intro exI[of _ r]) (auto simp: max_absorb2)
qed

lemma ennreal_Ex_less_of_nat: "(x::ennreal) < top ⟹ ∃n. x < of_nat n"
by (cases x rule: ennreal_cases)
(auto simp: ennreal_of_nat_eq_real_of_nat ennreal_less_iff reals_Archimedean2)

subsection ‹Coercion from \<^typ>‹ennreal› to \<^typ>‹real››

definition "enn2real x = real_of_ereal (enn2ereal x)"

lemma enn2real_nonneg[simp]: "0 ≤ enn2real x"
by (auto simp: enn2real_def intro!: real_of_ereal_pos enn2ereal_nonneg)

lemma enn2real_mono: "a ≤ b ⟹ b < top ⟹ enn2real a ≤ enn2real b"
by (auto simp add: enn2real_def less_eq_ennreal.rep_eq intro!: real_of_ereal_positive_mono enn2ereal_nonneg)

lemma enn2real_of_nat[simp]: "enn2real (of_nat n) = n"
by (auto simp: enn2real_def)

lemma enn2real_ennreal[simp]: "0 ≤ r ⟹ enn2real (ennreal r) = r"

lemma ennreal_enn2real[simp]: "r < top ⟹ ennreal (enn2real r) = r"
by (cases r rule: ennreal_cases) auto

lemma real_of_ereal_enn2ereal[simp]: "real_of_ereal (enn2ereal x) = enn2real x"

lemma enn2real_top[simp]: "enn2real top = 0"
unfolding enn2real_def top_ennreal.rep_eq top_ereal_def by simp

lemma enn2real_0[simp]: "enn2real 0 = 0"
unfolding enn2real_def zero_ennreal.rep_eq by simp

lemma enn2real_1[simp]: "enn2real 1 = 1"
unfolding enn2real_def one_ennreal.rep_eq by simp

lemma enn2real_numeral[simp]: "enn2real (numeral n) = (numeral n)"
unfolding enn2real_def by simp

lemma enn2real_mult: "enn2real (a * b) = enn2real a * enn2real b"
unfolding enn2real_def
by (simp del: real_of_ereal_enn2ereal add: times_ennreal.rep_eq)

lemma enn2real_leI: "0 ≤ B ⟹ x ≤ ennreal B ⟹ enn2real x ≤ B"
by (cases x rule: ennreal_cases) (auto simp: top_unique)

lemma enn2real_positive_iff: "0 < enn2real x ⟷ (0 < x ∧ x < top)"
by (cases x rule: ennreal_cases) auto

lemma enn2real_eq_posreal_iff[simp]: "c > 0 ⟹ enn2real x = c ⟷ x = c"
by (cases x) auto

lemma ennreal_enn2real_if: "ennreal (enn2real r) = (if r = top then 0 else r)"
by(auto intro!: ennreal_enn2real simp add: less_top)

subsection ‹Coercion from \<^typ>‹enat› to \<^typ>‹ennreal››

definition ennreal_of_enat :: "enat ⇒ ennreal"
where
"ennreal_of_enat n = (case n of ∞ ⇒ top | enat n ⇒ of_nat n)"

declare [[coercion ennreal_of_enat]]
declare [[coercion "of_nat :: nat ⇒ ennreal"]]

lemma ennreal_of_enat_infty[simp]: "ennreal_of_enat ∞ = ∞"

lemma ennreal_of_enat_enat[simp]: "ennreal_of_enat (enat n) = of_nat n"

lemma ennreal_of_enat_0[simp]: "ennreal_of_enat 0 = 0"
using ennreal_of_enat_enat[of 0] unfolding enat_0 by simp

lemma ennreal_of_enat_1[simp]: "ennreal_of_enat 1 = 1"
using ennreal_of_enat_enat[of 1] unfolding enat_1 by simp

lemma ennreal_top_neq_of_nat[simp]: "(top::ennreal) ≠ of_nat i"
using ennreal_of_nat_neq_top[of i] by metis

lemma ennreal_of_enat_inj[simp]: "ennreal_of_enat i = ennreal_of_enat j ⟷ i = j"
by (cases i j rule: enat.exhaust[case_product enat.exhaust]) auto

lemma ennreal_of_enat_le_iff[simp]: "ennreal_of_enat m ≤ ennreal_of_enat n ⟷ m ≤ n"
by (auto simp: ennreal_of_enat_def top_unique split: enat.split)

lemma of_nat_less_ennreal_of_nat[simp]: "of_nat n ≤ ennreal_of_enat x ⟷ of_nat n ≤ x"
by (cases x) (auto simp: of_nat_eq_enat)

lemma ennreal_of_enat_Sup: "ennreal_of_enat (Sup X) = (SUP x∈X. ennreal_of_enat x)"
proof -
have "ennreal_of_enat (Sup X) ≤ (SUP x ∈ X. ennreal_of_enat x)"
unfolding Sup_enat_def
proof (clarsimp, intro conjI impI)
fix x assume "finite X" "X ≠ {}"
then show "ennreal_of_enat (Max X) ≤ (SUP x ∈ X. ennreal_of_enat x)"
by (intro SUP_upper Max_in)
next
assume "infinite X" "X ≠ {}"
have "∃y∈X. r < ennreal_of_enat y" if r: "r < top" for r
proof -
obtain n where n: "r < of_nat n"
using ennreal_Ex_less_of_nat[OF r] ..
have "¬ (X ⊆ enat ` {.. n})"
using ‹infinite X› by (auto dest: finite_subset)
then obtain x where x: "x ∈ X" "x ∉ enat ` {..n}"
by blast
then have "of_nat n ≤ x"
by (cases x) (auto simp: of_nat_eq_enat)
with x show ?thesis
by (auto intro!: bexI[of _ x] less_le_trans[OF n])
qed
then have "(SUP x ∈ X. ennreal_of_enat x) = top"
by simp
then show "top ≤ (SUP x ∈ X. ennreal_of_enat x)"
unfolding top_unique by simp
qed
then show ?thesis
by (auto intro!: antisym Sup_least intro: Sup_upper)
qed

lemma ennreal_of_enat_eSuc[simp]: "ennreal_of_enat (eSuc x) = 1 + ennreal_of_enat x"
by (cases x) (auto simp: eSuc_enat)

(* Contributed by Dominique Unruh *)
lemma ennreal_of_enat_plus[simp]: ‹ennreal_of_enat (a+b) = ennreal_of_enat a + ennreal_of_enat b›
apply (induct a)
apply simp
done

(* Contributed by Dominique Unruh *)
lemma sum_ennreal_of_enat[simp]: "(∑i∈I. ennreal_of_enat (f i)) = ennreal_of_enat (sum f I)"
by (induct I rule: infinite_finite_induct) (auto simp: sum_nonneg)

subsection ‹Topology on \<^typ>‹ennreal››

lemma enn2ereal_Iio: "enn2ereal -` {..<a} = (if 0 ≤ a then {..< e2ennreal a} else {})"
using enn2ereal_nonneg
by (cases a rule: ereal_ennreal_cases)
(auto simp add: vimage_def set_eq_iff ennreal.enn2ereal_inverse less_ennreal.rep_eq e2ennreal_def max_absorb2
simp del: enn2ereal_nonneg
intro: le_less_trans less_imp_le)

lemma enn2ereal_Ioi: "enn2ereal -` {a <..} = (if 0 ≤ a then {e2ennreal a <..} else UNIV)"
by (cases a rule: ereal_ennreal_cases)
(auto simp add: vimage_def set_eq_iff ennreal.enn2ereal_inverse less_ennreal.rep_eq e2ennreal_def max_absorb2
intro: less_le_trans)

instantiation ennreal :: linear_continuum_topology
begin

definition open_ennreal :: "ennreal set ⇒ bool"
where "(open :: ennreal set ⇒ bool) = generate_topology (range lessThan ∪ range greaterThan)"

instance
proof
show "∃a b::ennreal. a ≠ b"
using zero_neq_one by (intro exI)
show "⋀x y::ennreal. x < y ⟹ ∃z>x. z < y"
proof transfer
fix x y :: ereal
assume *: "0 ≤ x"
assume "x < y"
from dense[OF this] obtain z where "x < z ∧ z < y" ..
with * show "∃z∈Collect ((≤) 0). x < z ∧ z < y"
by (intro bexI[of _ z]) auto
qed
qed (rule open_ennreal_def)

end

lemma continuous_on_e2ennreal: "continuous_on A e2ennreal"
proof (rule continuous_on_subset)
show "continuous_on ({0..} ∪ {..0}) e2ennreal"
proof (rule continuous_on_closed_Un)
show "continuous_on {0 ..} e2ennreal"
by (rule continuous_onI_mono)
(auto simp add: less_eq_ennreal.abs_eq eq_onp_def enn2ereal_range)
show "continuous_on {.. 0} e2ennreal"
by (subst continuous_on_cong[OF refl, of _ _ "λ_. 0"])
qed auto
show "A ⊆ {0..} ∪ {..0::ereal}"
by auto
qed

lemma continuous_at_e2ennreal: "continuous (at x within A) e2ennreal"
by (rule continuous_on_imp_continuous_within[OF continuous_on_e2ennreal, of _ UNIV]) auto

lemma continuous_on_enn2ereal: "continuous_on UNIV enn2ereal"
by (rule continuous_on_generate_topology[OF open_generated_order])

lemma continuous_at_enn2ereal: "continuous (at x within A) enn2ereal"
by (rule continuous_on_imp_continuous_within[OF continuous_on_enn2ereal]) auto

lemma sup_continuous_e2ennreal[order_continuous_intros]:
assumes f: "sup_continuous f" shows "sup_continuous (λx. e2ennreal (f x))"
proof (rule sup_continuous_compose[OF _ f])
show "sup_continuous e2ennreal"
by (simp add: continuous_at_e2ennreal continuous_at_left_imp_sup_continuous e2ennreal_mono mono_def)
qed

lemma sup_continuous_enn2ereal[order_continuous_intros]:
assumes f: "sup_continuous f" shows "sup_continuous (λx. enn2ereal (f x))"
proof (rule sup_continuous_compose[OF _ f])
show "sup_continuous enn2ereal"
by (simp add: continuous_at_enn2ereal continuous_at_left_imp_sup_continuous less_eq_ennreal.rep_eq mono_def)
qed

lemma sup_continuous_mult_left_ennreal':
fixes c :: "ennreal"
shows "sup_continuous (λx. c * x)"
unfolding sup_continuous_def
by transfer (auto simp: SUP_ereal_mult_left max.absorb2 SUP_upper2)

lemma sup_continuous_mult_left_ennreal[order_continuous_intros]:
"sup_continuous f ⟹ sup_continuous (λx. c * f x :: ennreal)"
by (rule sup_continuous_compose[OF sup_continuous_mult_left_ennreal'])

lemma sup_continuous_mult_right_ennreal[order_continuous_intros]:
"sup_continuous f ⟹ sup_continuous (λx. f x * c :: ennreal)"
using sup_continuous_mult_left_ennreal[of f c] by (simp add: mult.commute)

lemma sup_continuous_divide_ennreal[order_continuous_intros]:
fixes f g :: "'a::complete_lattice ⇒ ennreal"
shows "sup_continuous f ⟹ sup_continuous (λx. f x / c)"
unfolding divide_ennreal_def by (rule sup_continuous_mult_right_ennreal)

lemma transfer_enn2ereal_continuous_on [transfer_rule]:
"rel_fun (=) (rel_fun (rel_fun (=) pcr_ennreal) (=)) continuous_on continuous_on"
proof -
have "continuous_on A f" if "continuous_on A (λx. enn2ereal (f x))" for A and f :: "'a ⇒ ennreal"
using continuous_on_compose2[OF continuous_on_e2ennreal[of "{0..}"] that]
by (auto simp: ennreal.enn2ereal_inverse subset_eq e2ennreal_def max_absorb2)
moreover
have "continuous_on A (λx. enn2ereal (f x))" if "continuous_on A f" for A and f :: "'a ⇒ ennreal"
using continuous_on_compose2[OF continuous_on_enn2ereal that] by auto
ultimately
show ?thesis
by (auto simp add: rel_fun_def ennreal.pcr_cr_eq cr_ennreal_def)
qed

lemma transfer_sup_continuous[transfer_rule]:
"(rel_fun (rel_fun (=) pcr_ennreal) (=)) sup_continuous sup_continuous"
proof (safe intro!: rel_funI dest!: rel_fun_eq_pcr_ennreal[THEN iffD1])
show "sup_continuous (enn2ereal ∘ f) ⟹ sup_continuous f" for f :: "'a ⇒ _"
using sup_continuous_e2ennreal[of "enn2ereal ∘ f"] by simp
show "sup_continuous f ⟹ sup_continuous (enn2ereal ∘ f)" for f :: "'a ⇒ _"
using sup_continuous_enn2ereal[of f] by (simp add: comp_def)
qed

lemma continuous_on_ennreal[tendsto_intros]:
"continuous_on A f ⟹ continuous_on A (λx. ennreal (f x))"
by transfer (auto intro!: continuous_on_max continuous_on_const continuous_on_ereal)

lemma tendsto_ennrealD:
assumes lim: "((λx. ennreal (f x)) ⤏ ennreal x) F"
assumes *: "∀⇩F x in F. 0 ≤ f x" and x: "0 ≤ x"
shows "(f ⤏ x) F"
proof -
have "((λx. enn2ereal (ennreal (f x))) ⤏ enn2ereal (ennreal x)) F
⟷ (f ⤏ enn2ereal (ennreal x)) F"
using "*" eventually_mono
by (intro tendsto_cong) fastforce
then show ?thesis
using assms(1) continuous_at_enn2ereal isCont_tendsto_compose x by fastforce
qed

lemma tendsto_ennreal_iff [simp]:
‹((λx. ennreal (f x)) ⤏ ennreal x) F ⟷ (f ⤏ x) F› (is ‹?P ⟷ ?Q›)
if ‹∀⇩F x in F. 0 ≤ f x› ‹0 ≤ x›
proof
assume ‹?P›
then show ‹?Q›
using that by (rule tendsto_ennrealD)
next
assume ‹?Q›
have ‹continuous_on UNIV ereal›
using continuous_on_ereal [of _ id] by simp
then have ‹continuous_on UNIV (e2ennreal ∘ ereal)›
by (rule continuous_on_compose) (simp_all add: continuous_on_e2ennreal)
then have ‹((λx. (e2ennreal ∘ ereal) (f x)) ⤏ (e2ennreal ∘ ereal) x) F›
using ‹?Q› by (rule continuous_on_tendsto_compose) simp_all
then show ‹?P›
by (simp flip: e2ennreal_ereal)
qed

lemma tendsto_enn2ereal_iff[simp]: "((λi. enn2ereal (f i)) ⤏ enn2ereal x) F ⟷ (f ⤏ x) F"
using continuous_on_enn2ereal[THEN continuous_on_tendsto_compose, of f x F]
continuous_on_e2ennreal[THEN continuous_on_tendsto_compose, of "λx. enn2ereal (f x)" "enn2ereal x" F UNIV]
by auto

lemma ennreal_tendsto_0_iff: "(⋀n. f n ≥ 0) ⟹ ((λn. ennreal (f n)) ⇢ 0) ⟷ (f ⇢ 0)"
by (metis (mono_tags) ennreal_0 eventuallyI order_refl tendsto_ennreal_iff)

fixes f g :: "'a::topological_space ⇒ ennreal"
shows "continuous_on A f ⟹ continuous_on A g ⟹ continuous_on A (λx. f x + g x)"
by (transfer fixing: A) (auto intro!: tendsto_add_ereal_nonneg simp: continuous_on_def)

lemma continuous_on_inverse_ennreal[continuous_intros]:
fixes f :: "'a::topological_space ⇒ ennreal"
shows "continuous_on A f ⟹ continuous_on A (λx. inverse (f x))"
proof (transfer fixing: A)
show "pred_fun top  ((≤) 0) f ⟹ continuous_on A (λx. inverse (f x))" if "continuous_on A f"
for f :: "'a ⇒ ereal"
using continuous_on_compose2[OF continuous_on_inverse_ereal that] by (auto simp: subset_eq)
qed

proof
show "((λx. fst x + snd x) ⤏ a + b) (nhds a ×⇩F nhds b)" for a b :: ennreal
using tendsto_at_iff_tendsto_nhds[symmetric, of "λx::(ennreal × ennreal). fst x + snd x"]
by (auto simp: continuous_on_eq_continuous_at)
qed

fixes f g :: "'a::complete_lattice ⇒ ennreal"
shows "sup_continuous f ⟹ sup_continuous g ⟹ sup_continuous (λx. f x + g x)"

lemma ennreal_suminf_lessD: "(∑i. f i :: ennreal) < x ⟹ f i < x"
using le_less_trans[OF sum_le_suminf[OF summableI, of "{i}" f]] by simp

lemma sums_ennreal[simp]: "(⋀i. 0 ≤ f i) ⟹ 0 ≤ x ⟹ (λi. ennreal (f i)) sums ennreal x ⟷ f sums x"
unfolding sums_def by (simp add: always_eventually sum_nonneg)

lemma summable_suminf_not_top: "(⋀i. 0 ≤ f i) ⟹ (∑i. ennreal (f i)) ≠ top ⟹ summable f"
using summable_sums[OF summableI, of "λi. ennreal (f i)"]
by (cases "∑i. ennreal (f i)" rule: ennreal_cases)
(auto simp: summable_def)

lemma suminf_ennreal[simp]:
"(⋀i. 0 ≤ f i) ⟹ (∑i. ennreal (f i)) ≠ top ⟹ (∑i. ennreal (f i)) = ennreal (∑i. f i)"
by (rule sums_unique[symmetric]) (simp add: summable_suminf_not_top suminf_nonneg summable_sums)

lemma sums_enn2ereal[simp]: "(λi. enn2ereal (f i)) sums enn2ereal x ⟷ f sums x"
unfolding sums_def by (simp add: always_eventually sum_nonneg)

lemma suminf_enn2ereal[simp]: "(∑i. enn2ereal (f i)) = enn2ereal (suminf f)"
by (rule sums_unique[symmetric]) (simp add: summable_sums)

lemma transfer_e2ennreal_suminf [transfer_rule]: "rel_fun (rel_fun (=) pcr_ennreal) pcr_ennreal suminf suminf"
by (auto simp: rel_funI rel_fun_eq_pcr_ennreal comp_def)

lemma ennreal_suminf_cmult[simp]: "(∑i. r * f i) = r * (∑i. f i::ennreal)"
by transfer (auto intro!: suminf_cmult_ereal)

lemma ennreal_suminf_multc[simp]: "(∑i. f i * r) = (∑i. f i::ennreal) * r"
using ennreal_suminf_cmult[of r f] by (simp add: ac_simps)

lemma ennreal_suminf_divide[simp]: "(∑i. f i / r) = (∑i. f i::ennreal) / r"

lemma ennreal_suminf_neq_top: "summable f ⟹ (⋀i. 0 ≤ f i) ⟹ (∑i. ennreal (f i)) ≠ top"
using sums_ennreal[of f "suminf f"]
by (simp add: suminf_nonneg flip: sums_unique summable_sums_iff del: sums_ennreal)

lemma suminf_ennreal_eq:
"(⋀i. 0 ≤ f i) ⟹ f sums x ⟹ (∑i. ennreal (f i)) = ennreal x"
using suminf_nonneg[of f] sums_unique[of f x]
by (intro sums_unique[symmetric]) (auto simp: summable_sums_iff)

fixes f :: "nat ⇒ ennreal"
shows "(⋀N. (∑n<N. f n) + y ≤ x) ⟹ suminf f + y ≤ x"

lemma ennreal_suminf_SUP_eq_directed:
fixes f :: "'a ⇒ nat ⇒ ennreal"
assumes *: "⋀N i j. i ∈ I ⟹ j ∈ I ⟹ finite N ⟹ ∃k∈I. ∀n∈N. f i n ≤ f k n ∧ f j n ≤ f k n"
shows "(∑n. SUP i∈I. f i n) = (SUP i∈I. ∑n. f i n)"
proof cases
assume "I ≠ {}"
then obtain i where "i ∈ I" by auto
from * show ?thesis
by (transfer fixing: I)
(auto simp: max_absorb2 SUP_upper2[OF ‹i ∈ I›] suminf_nonneg summable_ereal_pos ‹I ≠ {}›
intro!: suminf_SUP_eq_directed)

fixes f g :: "nat ⇒ ennreal"
shows "(INF i. f i + c) = (INF i. f i) + c"
using continuous_at_Inf_mono[of "λx. x + c" "f`UNIV"]
using continuous_add[of "at_right (Inf (range f))", of "λx. x" "λx. c"]
by (auto simp: mono_def image_comp)