Theory Orders (Isabelle2005: October 2005)

# Theory Orders

Up to index of Isabelle/HOL/Lattice

theory Orders
imports Main
begin

    (*  Title:      HOL/Lattice/Orders.thy
        ID:         $Id: Orders.thy,v 1.6 2005/06/17 14:13:08 haftmann Exp $
        Author:     Markus Wenzel, TU Muenchen
    *)

    header {* Orders *}

    theory Orders imports Main begin

    subsection {* Ordered structures *}

    text {*
      We define several classes of ordered structures over some type @{typ
      'a} with relation @{text "\<sqsubseteq> :: '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).
    *}

    axclass leq < type
    consts
      leq :: "'a::leq => 'a => bool"  (infixl "[=" 50)
    syntax (xsymbols)
      leq :: "'a::leq => 'a => bool"  (infixl "\<sqsubseteq>" 50)

    axclass quasi_order < leq
      leq_refl [intro?]: "x \<sqsubseteq> x"
      leq_trans [trans]: "x \<sqsubseteq> y ==> y \<sqsubseteq> z ==> x \<sqsubseteq> z"

    axclass partial_order < quasi_order
      leq_antisym [trans]: "x \<sqsubseteq> y ==> y \<sqsubseteq> x ==> x = y"

    axclass linear_order < partial_order
      leq_linear: "x \<sqsubseteq> y ∨ y \<sqsubseteq> x"

    lemma linear_order_cases:
        "((x::'a::linear_order) \<sqsubseteq> y ==> C) ==> (y \<sqsubseteq> 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 @{text \<sqsubseteq>} relation defined as the inverse
      of the original one.
    *}

    datatype 'a dual = dual 'a

    consts
      undual :: "'a dual => 'a"
    primrec
      undual_dual: "undual (dual x) = x"

    instance dual :: (leq) leq ..

    defs (overloaded)
      leq_dual_def: "x' \<sqsubseteq> y' ≡ undual y' \<sqsubseteq> undual x'"

    lemma undual_leq [iff?]: "(undual x' \<sqsubseteq> undual y') = (y' \<sqsubseteq> x')"
      by (simp add: leq_dual_def)

    lemma dual_leq [iff?]: "(dual x \<sqsubseteq> dual y) = (y \<sqsubseteq> 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_compose [symmetric])
        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]: "dual ` UNIV = UNIV"
    proof (rule surj_range)
      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' \<sqsubseteq> undual x'" .. thus "x' \<sqsubseteq> x'" ..
      assume "y' \<sqsubseteq> z'" hence "undual z' \<sqsubseteq> undual y'" ..
      also assume "x' \<sqsubseteq> y'" hence "undual y' \<sqsubseteq> undual x'" ..
      finally show "x' \<sqsubseteq> z'" ..
    qed

    instance dual :: (partial_order) partial_order
    proof
      fix x' y' :: "'a::partial_order dual"
      assume "y' \<sqsubseteq> x'" hence "undual x' \<sqsubseteq> undual y'" ..
      also assume "x' \<sqsubseteq> y'" hence "undual y' \<sqsubseteq> undual x'" ..
      finally show "x' = y'" ..
    qed

    instance dual :: (linear_order) linear_order
    proof
      fix x' y' :: "'a::linear_order dual"
      show "x' \<sqsubseteq> y' ∨ y' \<sqsubseteq> x'"
      proof (rule linear_order_cases)
        assume "undual y' \<sqsubseteq> undual x'"
        hence "x' \<sqsubseteq> y'" .. thus ?thesis ..
      next
        assume "undual x' \<sqsubseteq> undual y'"
        hence "y' \<sqsubseteq> 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.
    *}

    instance * :: (leq, leq) leq ..

    defs (overloaded)
      leq_prod_def: "p \<sqsubseteq> q ≡ fst p \<sqsubseteq> fst q ∧ snd p \<sqsubseteq> snd q"

    lemma leq_prodI [intro?]:
        "fst p \<sqsubseteq> fst q ==> snd p \<sqsubseteq> snd q ==> p \<sqsubseteq> q"
      by (unfold leq_prod_def) blast

    lemma leq_prodE [elim?]:
        "p \<sqsubseteq> q ==> (fst p \<sqsubseteq> fst q ==> snd p \<sqsubseteq> snd q ==> C) ==> C"
      by (unfold leq_prod_def) blast

    instance * :: (quasi_order, quasi_order) quasi_order
    proof
      fix p q r :: "'a::quasi_order × 'b::quasi_order"
      show "p \<sqsubseteq> p"
      proof
        show "fst p \<sqsubseteq> fst p" ..
        show "snd p \<sqsubseteq> snd p" ..
      qed
      assume pq: "p \<sqsubseteq> q" and qr: "q \<sqsubseteq> r"
      show "p \<sqsubseteq> r"
      proof
        from pq have "fst p \<sqsubseteq> fst q" ..
        also from qr have "… \<sqsubseteq> fst r" ..
        finally show "fst p \<sqsubseteq> fst r" .
        from pq have "snd p \<sqsubseteq> snd q" ..
        also from qr have "… \<sqsubseteq> snd r" ..
        finally show "snd p \<sqsubseteq> snd r" .
      qed
    qed

    instance * :: (partial_order, partial_order) partial_order
    proof
      fix p q :: "'a::partial_order × 'b::partial_order"
      assume pq: "p \<sqsubseteq> q" and qp: "q \<sqsubseteq> p"
      show "p = q"
      proof
        from pq have "fst p \<sqsubseteq> fst q" ..
        also from qp have "… \<sqsubseteq> fst p" ..
        finally show "fst p = fst q" .
        from pq have "snd p \<sqsubseteq> snd q" ..
        also from qp have "… \<sqsubseteq> 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.
    *}

    instance fun :: (type, leq) leq ..

    defs (overloaded)
      leq_fun_def: "f \<sqsubseteq> g ≡ ∀x. f x \<sqsubseteq> g x"

    lemma leq_funI [intro?]: "(!!x. f x \<sqsubseteq> g x) ==> f \<sqsubseteq> g"
      by (unfold leq_fun_def) blast

    lemma leq_funD [dest?]: "f \<sqsubseteq> g ==> f x \<sqsubseteq> 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 \<sqsubseteq> f"
      proof
        fix x show "f x \<sqsubseteq> f x" ..
      qed
      assume fg: "f \<sqsubseteq> g" and gh: "g \<sqsubseteq> h"
      show "f \<sqsubseteq> h"
      proof
        fix x from fg have "f x \<sqsubseteq> g x" ..
        also from gh have "… \<sqsubseteq> h x" ..
        finally show "f x \<sqsubseteq> h x" .
      qed
    qed

    instance fun :: (type, partial_order) partial_order
    proof
      fix f g :: "'a => 'b::partial_order"
      assume fg: "f \<sqsubseteq> g" and gf: "g \<sqsubseteq> f"
      show "f = g"
      proof
        fix x from fg have "f x \<sqsubseteq> g x" ..
        also from gf have "… \<sqsubseteq> f x" ..
        finally show "f x = g x" .
      qed
    qed

    end

### Ordered structures

lemma linear_order_cases:

      [| x [= y ==> C; y [= x ==> C |] ==> C

### Duality

lemma undual_leq:

      (undual x' [= undual y') = (y' [= x')

lemma dual_leq:

      (dual x [= dual y) = (y [= x)

lemma dual_undual:

      dual (undual x') = x'

lemma undual_dual_id:

      undual o dual = id

lemma dual_undual_id:

      dual o undual = id

lemma undual_equality:

      (undual x' = undual y') = (x' = y')

lemma dual_equality:

      (dual x = dual y) = (x = y)

lemma dual_ball:

      (∀x∈A. P (dual x)) = (∀x'∈dual ` A. P x')

lemma range_dual:

      range dual = UNIV

lemma dual_all:

      (∀x. P (dual x)) = (∀x'. P x')

lemma dual_ex:

      (∃x. P (dual x)) = (∃x'. P x')

lemma dual_Collect:

      {dual x |x. P (dual x)} = {x'. P x'}

### Transforming orders

#### Duals

#### Binary products \label{sec:prod-order}

lemma leq_prodI:

      [| fst p [= fst q; snd p [= snd q |] ==> p [= q

lemma leq_prodE:

      [| p [= q; [| fst p [= fst q; snd p [= snd q |] ==> C |] ==> C

#### General products \label{sec:fun-order}

lemma leq_funI:

      (!!x. f x [= g x) ==> f [= g

lemma leq_funD:

      f [= g ==> f x [= g x