(* Title: HOL/Lattice/Orders.thy Author: Markus Wenzel, TU Muenchen *) section ‹Orders› theory Orders imports Main begin subsection ‹Ordered structures› text ‹ We define several classes of ordered structures over some type @{typ 'a} with relation ‹⊑ :: 'a ⇒ 'a ⇒ bool›. For a \emph{quasi-order} that relation is required to be reflexive and transitive, for a \emph{partial order} it also has to be anti-symmetric, while for a \emph{linear order} all elements are required to be related (in either direction). › class leq = fixes leq :: "'a ⇒ 'a ⇒ bool" (infixl "⊑" 50) class quasi_order = leq + assumes leq_refl [intro?]: "x ⊑ x" assumes leq_trans [trans]: "x ⊑ y ⟹ y ⊑ z ⟹ x ⊑ z" class partial_order = quasi_order + assumes leq_antisym [trans]: "x ⊑ y ⟹ y ⊑ x ⟹ x = y" class linear_order = partial_order + assumes leq_linear: "x ⊑ y ∨ y ⊑ x" lemma linear_order_cases: "((x::'a::linear_order) ⊑ y ⟹ C) ⟹ (y ⊑ x ⟹ C) ⟹ C" by (insert leq_linear) blast subsection ‹Duality› text ‹ The \emph{dual} of an ordered structure is an isomorphic copy of the underlying type, with the ‹⊑› relation defined as the inverse of the original one. › datatype 'a dual = dual 'a primrec undual :: "'a dual ⇒ 'a" where undual_dual: "undual (dual x) = x" instantiation dual :: (leq) leq begin definition leq_dual_def: "x' ⊑ y' ≡ undual y' ⊑ undual x'" instance .. end lemma undual_leq [iff?]: "(undual x' ⊑ undual y') = (y' ⊑ x')" by (simp add: leq_dual_def) lemma dual_leq [iff?]: "(dual x ⊑ dual y) = (y ⊑ x)" by (simp add: leq_dual_def) text ‹ \medskip Functions @{term dual} and @{term undual} are inverse to each other; this entails the following fundamental properties. › lemma dual_undual [simp]: "dual (undual x') = x'" by (cases x') simp lemma undual_dual_id [simp]: "undual o dual = id" by (rule ext) simp lemma dual_undual_id [simp]: "dual o undual = id" by (rule ext) simp text ‹ \medskip Since @{term dual} (and @{term undual}) are both injective and surjective, the basic logical connectives (equality, quantification etc.) are transferred as follows. › lemma undual_equality [iff?]: "(undual x' = undual y') = (x' = y')" by (cases x', cases y') simp lemma dual_equality [iff?]: "(dual x = dual y) = (x = y)" by simp lemma dual_ball [iff?]: "(∀x ∈ A. P (dual x)) = (∀x' ∈ dual ` A. P x')" proof assume a: "∀x ∈ A. P (dual x)" show "∀x' ∈ dual ` A. P x'" proof fix x' assume x': "x' ∈ dual ` A" have "undual x' ∈ A" proof - from x' have "undual x' ∈ undual ` dual ` A" by simp thus "undual x' ∈ A" by (simp add: image_comp) qed with a have "P (dual (undual x'))" .. also have "… = x'" by simp finally show "P x'" . qed next assume a: "∀x' ∈ dual ` A. P x'" show "∀x ∈ A. P (dual x)" proof fix x assume "x ∈ A" hence "dual x ∈ dual ` A" by simp with a show "P (dual x)" .. qed qed lemma range_dual [simp]: "surj dual" proof - have "⋀x'. dual (undual x') = x'" by simp thus "surj dual" by (rule surjI) qed lemma dual_all [iff?]: "(∀x. P (dual x)) = (∀x'. P x')" proof - have "(∀x ∈ UNIV. P (dual x)) = (∀x' ∈ dual ` UNIV. P x')" by (rule dual_ball) thus ?thesis by simp qed lemma dual_ex: "(∃x. P (dual x)) = (∃x'. P x')" proof - have "(∀x. ¬ P (dual x)) = (∀x'. ¬ P x')" by (rule dual_all) thus ?thesis by blast qed lemma dual_Collect: "{dual x| x. P (dual x)} = {x'. P x'}" proof - have "{dual x| x. P (dual x)} = {x'. ∃x''. x' = x'' ∧ P x''}" by (simp only: dual_ex [symmetric]) thus ?thesis by blast qed subsection ‹Transforming orders› subsubsection ‹Duals› text ‹ The classes of quasi, partial, and linear orders are all closed under formation of dual structures. › instance dual :: (quasi_order) quasi_order proof fix x' y' z' :: "'a::quasi_order dual" have "undual x' ⊑ undual x'" .. thus "x' ⊑ x'" .. assume "y' ⊑ z'" hence "undual z' ⊑ undual y'" .. also assume "x' ⊑ y'" hence "undual y' ⊑ undual x'" .. finally show "x' ⊑ z'" .. qed instance dual :: (partial_order) partial_order proof fix x' y' :: "'a::partial_order dual" assume "y' ⊑ x'" hence "undual x' ⊑ undual y'" .. also assume "x' ⊑ y'" hence "undual y' ⊑ undual x'" .. finally show "x' = y'" .. qed instance dual :: (linear_order) linear_order proof fix x' y' :: "'a::linear_order dual" show "x' ⊑ y' ∨ y' ⊑ x'" proof (rule linear_order_cases) assume "undual y' ⊑ undual x'" hence "x' ⊑ y'" .. thus ?thesis .. next assume "undual x' ⊑ undual y'" hence "y' ⊑ x'" .. thus ?thesis .. qed qed subsubsection ‹Binary products \label{sec:prod-order}› text ‹ The classes of quasi and partial orders are closed under binary products. Note that the direct product of linear orders need \emph{not} be linear in general. › instantiation prod :: (leq, leq) leq begin definition leq_prod_def: "p ⊑ q ≡ fst p ⊑ fst q ∧ snd p ⊑ snd q" instance .. end lemma leq_prodI [intro?]: "fst p ⊑ fst q ⟹ snd p ⊑ snd q ⟹ p ⊑ q" by (unfold leq_prod_def) blast lemma leq_prodE [elim?]: "p ⊑ q ⟹ (fst p ⊑ fst q ⟹ snd p ⊑ snd q ⟹ C) ⟹ C" by (unfold leq_prod_def) blast instance prod :: (quasi_order, quasi_order) quasi_order proof fix p q r :: "'a::quasi_order × 'b::quasi_order" show "p ⊑ p" proof show "fst p ⊑ fst p" .. show "snd p ⊑ snd p" .. qed assume pq: "p ⊑ q" and qr: "q ⊑ r" show "p ⊑ r" proof from pq have "fst p ⊑ fst q" .. also from qr have "… ⊑ fst r" .. finally show "fst p ⊑ fst r" . from pq have "snd p ⊑ snd q" .. also from qr have "… ⊑ snd r" .. finally show "snd p ⊑ snd r" . qed qed instance prod :: (partial_order, partial_order) partial_order proof fix p q :: "'a::partial_order × 'b::partial_order" assume pq: "p ⊑ q" and qp: "q ⊑ p" show "p = q" proof from pq have "fst p ⊑ fst q" .. also from qp have "… ⊑ fst p" .. finally show "fst p = fst q" . from pq have "snd p ⊑ snd q" .. also from qp have "… ⊑ snd p" .. finally show "snd p = snd q" . qed qed subsubsection ‹General products \label{sec:fun-order}› text ‹ The classes of quasi and partial orders are closed under general products (function spaces). Note that the direct product of linear orders need \emph{not} be linear in general. › instantiation "fun" :: (type, leq) leq begin definition leq_fun_def: "f ⊑ g ≡ ∀x. f x ⊑ g x" instance .. end lemma leq_funI [intro?]: "(⋀x. f x ⊑ g x) ⟹ f ⊑ g" by (unfold leq_fun_def) blast lemma leq_funD [dest?]: "f ⊑ g ⟹ f x ⊑ g x" by (unfold leq_fun_def) blast instance "fun" :: (type, quasi_order) quasi_order proof fix f g h :: "'a ⇒ 'b::quasi_order" show "f ⊑ f" proof fix x show "f x ⊑ f x" .. qed assume fg: "f ⊑ g" and gh: "g ⊑ h" show "f ⊑ h" proof fix x from fg have "f x ⊑ g x" .. also from gh have "… ⊑ h x" .. finally show "f x ⊑ h x" . qed qed instance "fun" :: (type, partial_order) partial_order proof fix f g :: "'a ⇒ 'b::partial_order" assume fg: "f ⊑ g" and gf: "g ⊑ f" show "f = g" proof fix x from fg have "f x ⊑ g x" .. also from gf have "… ⊑ f x" .. finally show "f x = g x" . qed qed end