src/HOL/Algebra/Lattice.thy
author ballarin
Tue Jul 04 14:47:01 2006 +0200 (2006-07-04)
changeset 19984 29bb4659f80a
parent 19931 fb32b43e7f80
child 20318 0e0ea63fe768
permissions -rw-r--r--
Method intro_locales replaced by intro_locales and unfold_locales.
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(*
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  Title:     HOL/Algebra/Lattice.thy
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  Id:        $Id$
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  Author:    Clemens Ballarin, started 7 November 2003
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  Copyright: Clemens Ballarin
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*)
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header {* Orders and Lattices *}
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theory Lattice imports Main begin
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text {* Object with a carrier set. *}
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record 'a partial_object =
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  carrier :: "'a set"
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subsection {* Partial Orders *}
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record 'a order = "'a partial_object" +
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  le :: "['a, 'a] => bool" (infixl "\<sqsubseteq>\<index>" 50)
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locale partial_order =
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  fixes L (structure)
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  assumes refl [intro, simp]:
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                  "x \<in> carrier L ==> x \<sqsubseteq> x"
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    and anti_sym [intro]:
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                  "[| x \<sqsubseteq> y; y \<sqsubseteq> x; x \<in> carrier L; y \<in> carrier L |] ==> x = y"
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    and trans [trans]:
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                  "[| x \<sqsubseteq> y; y \<sqsubseteq> z;
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                   x \<in> carrier L; y \<in> carrier L; z \<in> carrier L |] ==> x \<sqsubseteq> z"
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constdefs (structure L)
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  lless :: "[_, 'a, 'a] => bool" (infixl "\<sqsubset>\<index>" 50)
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  "x \<sqsubset> y == x \<sqsubseteq> y & x ~= y"
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  -- {* Upper and lower bounds of a set. *}
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  Upper :: "[_, 'a set] => 'a set"
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  "Upper L A == {u. (ALL x. x \<in> A \<inter> carrier L --> x \<sqsubseteq> u)} \<inter>
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                carrier L"
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  Lower :: "[_, 'a set] => 'a set"
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  "Lower L A == {l. (ALL x. x \<in> A \<inter> carrier L --> l \<sqsubseteq> x)} \<inter>
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                carrier L"
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  -- {* Least and greatest, as predicate. *}
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  least :: "[_, 'a, 'a set] => bool"
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  "least L l A == A \<subseteq> carrier L & l \<in> A & (ALL x : A. l \<sqsubseteq> x)"
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  greatest :: "[_, 'a, 'a set] => bool"
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  "greatest L g A == A \<subseteq> carrier L & g \<in> A & (ALL x : A. x \<sqsubseteq> g)"
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  -- {* Supremum and infimum *}
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  sup :: "[_, 'a set] => 'a" ("\<Squnion>\<index>_" [90] 90)
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  "\<Squnion>A == THE x. least L x (Upper L A)"
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  inf :: "[_, 'a set] => 'a" ("\<Sqinter>\<index>_" [90] 90)
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  "\<Sqinter>A == THE x. greatest L x (Lower L A)"
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  join :: "[_, 'a, 'a] => 'a" (infixl "\<squnion>\<index>" 65)
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  "x \<squnion> y == sup L {x, y}"
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  meet :: "[_, 'a, 'a] => 'a" (infixl "\<sqinter>\<index>" 70)
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  "x \<sqinter> y == inf L {x, y}"
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subsubsection {* Upper *}
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lemma Upper_closed [intro, simp]:
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  "Upper L A \<subseteq> carrier L"
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  by (unfold Upper_def) clarify
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lemma UpperD [dest]:
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  fixes L (structure)
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  shows "[| u \<in> Upper L A; x \<in> A; A \<subseteq> carrier L |] ==> x \<sqsubseteq> u"
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  by (unfold Upper_def) blast
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lemma Upper_memI:
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  fixes L (structure)
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  shows "[| !! y. y \<in> A ==> y \<sqsubseteq> x; x \<in> carrier L |] ==> x \<in> Upper L A"
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  by (unfold Upper_def) blast
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lemma Upper_antimono:
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  "A \<subseteq> B ==> Upper L B \<subseteq> Upper L A"
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  by (unfold Upper_def) blast
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subsubsection {* Lower *}
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lemma Lower_closed [intro, simp]:
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  "Lower L A \<subseteq> carrier L"
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  by (unfold Lower_def) clarify
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lemma LowerD [dest]:
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  fixes L (structure)
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  shows "[| l \<in> Lower L A; x \<in> A; A \<subseteq> carrier L |] ==> l \<sqsubseteq> x"
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  by (unfold Lower_def) blast
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lemma Lower_memI:
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  fixes L (structure)
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  shows "[| !! y. y \<in> A ==> x \<sqsubseteq> y; x \<in> carrier L |] ==> x \<in> Lower L A"
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  by (unfold Lower_def) blast
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lemma Lower_antimono:
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  "A \<subseteq> B ==> Lower L B \<subseteq> Lower L A"
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  by (unfold Lower_def) blast
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subsubsection {* least *}
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lemma least_carrier [intro, simp]:
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  shows "least L l A ==> l \<in> carrier L"
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  by (unfold least_def) fast
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lemma least_mem:
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  "least L l A ==> l \<in> A"
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  by (unfold least_def) fast
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lemma (in partial_order) least_unique:
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  "[| least L x A; least L y A |] ==> x = y"
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  by (unfold least_def) blast
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lemma least_le:
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  fixes L (structure)
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  shows "[| least L x A; a \<in> A |] ==> x \<sqsubseteq> a"
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  by (unfold least_def) fast
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lemma least_UpperI:
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  fixes L (structure)
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  assumes above: "!! x. x \<in> A ==> x \<sqsubseteq> s"
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    and below: "!! y. y \<in> Upper L A ==> s \<sqsubseteq> y"
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    and L: "A \<subseteq> carrier L"  "s \<in> carrier L"
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  shows "least L s (Upper L A)"
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proof -
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  have "Upper L A \<subseteq> carrier L" by simp
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  moreover from above L have "s \<in> Upper L A" by (simp add: Upper_def)
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  moreover from below have "ALL x : Upper L A. s \<sqsubseteq> x" by fast
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  ultimately show ?thesis by (simp add: least_def)
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qed
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subsubsection {* greatest *}
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lemma greatest_carrier [intro, simp]:
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  shows "greatest L l A ==> l \<in> carrier L"
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  by (unfold greatest_def) fast
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lemma greatest_mem:
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  "greatest L l A ==> l \<in> A"
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  by (unfold greatest_def) fast
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lemma (in partial_order) greatest_unique:
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  "[| greatest L x A; greatest L y A |] ==> x = y"
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  by (unfold greatest_def) blast
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lemma greatest_le:
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  fixes L (structure)
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  shows "[| greatest L x A; a \<in> A |] ==> a \<sqsubseteq> x"
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  by (unfold greatest_def) fast
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lemma greatest_LowerI:
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  fixes L (structure)
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  assumes below: "!! x. x \<in> A ==> i \<sqsubseteq> x"
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    and above: "!! y. y \<in> Lower L A ==> y \<sqsubseteq> i"
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    and L: "A \<subseteq> carrier L"  "i \<in> carrier L"
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  shows "greatest L i (Lower L A)"
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proof -
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  have "Lower L A \<subseteq> carrier L" by simp
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  moreover from below L have "i \<in> Lower L A" by (simp add: Lower_def)
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  moreover from above have "ALL x : Lower L A. x \<sqsubseteq> i" by fast
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  ultimately show ?thesis by (simp add: greatest_def)
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qed
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subsection {* Lattices *}
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locale lattice = partial_order +
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  assumes sup_of_two_exists:
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    "[| x \<in> carrier L; y \<in> carrier L |] ==> EX s. least L s (Upper L {x, y})"
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    and inf_of_two_exists:
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    "[| x \<in> carrier L; y \<in> carrier L |] ==> EX s. greatest L s (Lower L {x, y})"
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lemma least_Upper_above:
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  fixes L (structure)
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  shows "[| least L s (Upper L A); x \<in> A; A \<subseteq> carrier L |] ==> x \<sqsubseteq> s"
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  by (unfold least_def) blast
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lemma greatest_Lower_above:
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  fixes L (structure)
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  shows "[| greatest L i (Lower L A); x \<in> A; A \<subseteq> carrier L |] ==> i \<sqsubseteq> x"
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  by (unfold greatest_def) blast
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subsubsection {* Supremum *}
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lemma (in lattice) joinI:
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  "[| !!l. least L l (Upper L {x, y}) ==> P l; x \<in> carrier L; y \<in> carrier L |]
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  ==> P (x \<squnion> y)"
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proof (unfold join_def sup_def)
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  assume L: "x \<in> carrier L"  "y \<in> carrier L"
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    and P: "!!l. least L l (Upper L {x, y}) ==> P l"
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  with sup_of_two_exists obtain s where "least L s (Upper L {x, y})" by fast
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  with L show "P (THE l. least L l (Upper L {x, y}))"
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    by (fast intro: theI2 least_unique P)
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qed
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lemma (in lattice) join_closed [simp]:
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  "[| x \<in> carrier L; y \<in> carrier L |] ==> x \<squnion> y \<in> carrier L"
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  by (rule joinI) (rule least_carrier)
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lemma (in partial_order) sup_of_singletonI:      (* only reflexivity needed ? *)
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  "x \<in> carrier L ==> least L x (Upper L {x})"
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  by (rule least_UpperI) fast+
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lemma (in partial_order) sup_of_singleton [simp]:
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  "x \<in> carrier L ==> \<Squnion>{x} = x"
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  by (unfold sup_def) (blast intro: least_unique least_UpperI sup_of_singletonI)
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text {* Condition on @{text A}: supremum exists. *}
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lemma (in lattice) sup_insertI:
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  "[| !!s. least L s (Upper L (insert x A)) ==> P s;
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  least L a (Upper L A); x \<in> carrier L; A \<subseteq> carrier L |]
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  ==> P (\<Squnion>(insert x A))"
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proof (unfold sup_def)
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  assume L: "x \<in> carrier L"  "A \<subseteq> carrier L"
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    and P: "!!l. least L l (Upper L (insert x A)) ==> P l"
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    and least_a: "least L a (Upper L A)"
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  from L least_a have La: "a \<in> carrier L" by simp
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  from L sup_of_two_exists least_a
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  obtain s where least_s: "least L s (Upper L {a, x})" by blast
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  show "P (THE l. least L l (Upper L (insert x A)))"
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  proof (rule theI2)
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    show "least L s (Upper L (insert x A))"
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    proof (rule least_UpperI)
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      fix z
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      assume "z \<in> insert x A"
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      then show "z \<sqsubseteq> s"
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      proof
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        assume "z = x" then show ?thesis
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          by (simp add: least_Upper_above [OF least_s] L La)
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      next
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        assume "z \<in> A"
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        with L least_s least_a show ?thesis
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          by (rule_tac trans [where y = a]) (auto dest: least_Upper_above)
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      qed
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    next
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      fix y
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      assume y: "y \<in> Upper L (insert x A)"
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      show "s \<sqsubseteq> y"
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      proof (rule least_le [OF least_s], rule Upper_memI)
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	fix z
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	assume z: "z \<in> {a, x}"
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	then show "z \<sqsubseteq> y"
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	proof
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          have y': "y \<in> Upper L A"
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            apply (rule subsetD [where A = "Upper L (insert x A)"])
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            apply (rule Upper_antimono) apply clarify apply assumption
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            done
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          assume "z = a"
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          with y' least_a show ?thesis by (fast dest: least_le)
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	next
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	  assume "z \<in> {x}"  (* FIXME "z = x"; declare specific elim rule for "insert x {}" (!?) *)
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          with y L show ?thesis by blast
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	qed
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      qed (rule Upper_closed [THEN subsetD])
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    next
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      from L show "insert x A \<subseteq> carrier L" by simp
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      from least_s show "s \<in> carrier L" by simp
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    qed
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  next
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    fix l
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    assume least_l: "least L l (Upper L (insert x A))"
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    show "l = s"
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    proof (rule least_unique)
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      show "least L s (Upper L (insert x A))"
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      proof (rule least_UpperI)
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        fix z
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        assume "z \<in> insert x A"
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        then show "z \<sqsubseteq> s"
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	proof
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          assume "z = x" then show ?thesis
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            by (simp add: least_Upper_above [OF least_s] L La)
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	next
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          assume "z \<in> A"
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          with L least_s least_a show ?thesis
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            by (rule_tac trans [where y = a]) (auto dest: least_Upper_above)
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	qed
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      next
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        fix y
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        assume y: "y \<in> Upper L (insert x A)"
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        show "s \<sqsubseteq> y"
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        proof (rule least_le [OF least_s], rule Upper_memI)
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          fix z
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          assume z: "z \<in> {a, x}"
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          then show "z \<sqsubseteq> y"
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          proof
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            have y': "y \<in> Upper L A"
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	      apply (rule subsetD [where A = "Upper L (insert x A)"])
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	      apply (rule Upper_antimono) apply clarify apply assumption
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	      done
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            assume "z = a"
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            with y' least_a show ?thesis by (fast dest: least_le)
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	  next
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            assume "z \<in> {x}"
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            with y L show ?thesis by blast
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          qed
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        qed (rule Upper_closed [THEN subsetD])
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      next
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        from L show "insert x A \<subseteq> carrier L" by simp
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        from least_s show "s \<in> carrier L" by simp
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      qed
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    qed
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  qed
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qed
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lemma (in lattice) finite_sup_least:
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  "[| finite A; A \<subseteq> carrier L; A ~= {} |] ==> least L (\<Squnion>A) (Upper L A)"
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proof (induct set: Finites)
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  case empty
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  then show ?case by simp
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next
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  case (insert x A)
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  show ?case
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  proof (cases "A = {}")
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    case True
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    with insert show ?thesis by (simp add: sup_of_singletonI)
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  next
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    case False
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    with insert have "least L (\<Squnion>A) (Upper L A)" by simp
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    with _ show ?thesis
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      by (rule sup_insertI) (simp_all add: insert [simplified])
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  qed
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qed
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lemma (in lattice) finite_sup_insertI:
ballarin@14551
   337
  assumes P: "!!l. least L l (Upper L (insert x A)) ==> P l"
wenzelm@14693
   338
    and xA: "finite A"  "x \<in> carrier L"  "A \<subseteq> carrier L"
ballarin@14551
   339
  shows "P (\<Squnion> (insert x A))"
ballarin@14551
   340
proof (cases "A = {}")
ballarin@14551
   341
  case True with P and xA show ?thesis
ballarin@14551
   342
    by (simp add: sup_of_singletonI)
ballarin@14551
   343
next
ballarin@14551
   344
  case False with P and xA show ?thesis
ballarin@14551
   345
    by (simp add: sup_insertI finite_sup_least)
ballarin@14551
   346
qed
ballarin@14551
   347
ballarin@14551
   348
lemma (in lattice) finite_sup_closed:
wenzelm@14693
   349
  "[| finite A; A \<subseteq> carrier L; A ~= {} |] ==> \<Squnion>A \<in> carrier L"
ballarin@14551
   350
proof (induct set: Finites)
ballarin@14551
   351
  case empty then show ?case by simp
ballarin@14551
   352
next
nipkow@15328
   353
  case insert then show ?case
wenzelm@14693
   354
    by - (rule finite_sup_insertI, simp_all)
ballarin@14551
   355
qed
ballarin@14551
   356
ballarin@14551
   357
lemma (in lattice) join_left:
ballarin@14551
   358
  "[| x \<in> carrier L; y \<in> carrier L |] ==> x \<sqsubseteq> x \<squnion> y"
wenzelm@14693
   359
  by (rule joinI [folded join_def]) (blast dest: least_mem)
ballarin@14551
   360
ballarin@14551
   361
lemma (in lattice) join_right:
ballarin@14551
   362
  "[| x \<in> carrier L; y \<in> carrier L |] ==> y \<sqsubseteq> x \<squnion> y"
wenzelm@14693
   363
  by (rule joinI [folded join_def]) (blast dest: least_mem)
ballarin@14551
   364
ballarin@14551
   365
lemma (in lattice) sup_of_two_least:
wenzelm@14693
   366
  "[| x \<in> carrier L; y \<in> carrier L |] ==> least L (\<Squnion>{x, y}) (Upper L {x, y})"
ballarin@14551
   367
proof (unfold sup_def)
wenzelm@14693
   368
  assume L: "x \<in> carrier L"  "y \<in> carrier L"
ballarin@14551
   369
  with sup_of_two_exists obtain s where "least L s (Upper L {x, y})" by fast
ballarin@14551
   370
  with L show "least L (THE xa. least L xa (Upper L {x, y})) (Upper L {x, y})"
ballarin@14551
   371
  by (fast intro: theI2 least_unique)  (* blast fails *)
ballarin@14551
   372
qed
ballarin@14551
   373
ballarin@14551
   374
lemma (in lattice) join_le:
wenzelm@14693
   375
  assumes sub: "x \<sqsubseteq> z"  "y \<sqsubseteq> z"
wenzelm@14693
   376
    and L: "x \<in> carrier L"  "y \<in> carrier L"  "z \<in> carrier L"
ballarin@14551
   377
  shows "x \<squnion> y \<sqsubseteq> z"
ballarin@14551
   378
proof (rule joinI)
ballarin@14551
   379
  fix s
ballarin@14551
   380
  assume "least L s (Upper L {x, y})"
ballarin@14551
   381
  with sub L show "s \<sqsubseteq> z" by (fast elim: least_le intro: Upper_memI)
ballarin@14551
   382
qed
wenzelm@14693
   383
ballarin@14551
   384
lemma (in lattice) join_assoc_lemma:
wenzelm@14693
   385
  assumes L: "x \<in> carrier L"  "y \<in> carrier L"  "z \<in> carrier L"
wenzelm@14693
   386
  shows "x \<squnion> (y \<squnion> z) = \<Squnion>{x, y, z}"
ballarin@14551
   387
proof (rule finite_sup_insertI)
wenzelm@14651
   388
  -- {* The textbook argument in Jacobson I, p 457 *}
ballarin@14551
   389
  fix s
ballarin@14551
   390
  assume sup: "least L s (Upper L {x, y, z})"
ballarin@14551
   391
  show "x \<squnion> (y \<squnion> z) = s"
ballarin@14551
   392
  proof (rule anti_sym)
ballarin@14551
   393
    from sup L show "x \<squnion> (y \<squnion> z) \<sqsubseteq> s"
ballarin@14551
   394
      by (fastsimp intro!: join_le elim: least_Upper_above)
ballarin@14551
   395
  next
ballarin@14551
   396
    from sup L show "s \<sqsubseteq> x \<squnion> (y \<squnion> z)"
ballarin@14551
   397
    by (erule_tac least_le)
ballarin@14551
   398
      (blast intro!: Upper_memI intro: trans join_left join_right join_closed)
ballarin@14551
   399
  qed (simp_all add: L least_carrier [OF sup])
ballarin@14551
   400
qed (simp_all add: L)
ballarin@14551
   401
ballarin@14551
   402
lemma join_comm:
ballarin@19783
   403
  fixes L (structure)
ballarin@14551
   404
  shows "x \<squnion> y = y \<squnion> x"
ballarin@14551
   405
  by (unfold join_def) (simp add: insert_commute)
ballarin@14551
   406
ballarin@14551
   407
lemma (in lattice) join_assoc:
wenzelm@14693
   408
  assumes L: "x \<in> carrier L"  "y \<in> carrier L"  "z \<in> carrier L"
ballarin@14551
   409
  shows "(x \<squnion> y) \<squnion> z = x \<squnion> (y \<squnion> z)"
ballarin@14551
   410
proof -
ballarin@14551
   411
  have "(x \<squnion> y) \<squnion> z = z \<squnion> (x \<squnion> y)" by (simp only: join_comm)
wenzelm@14693
   412
  also from L have "... = \<Squnion>{z, x, y}" by (simp add: join_assoc_lemma)
wenzelm@14693
   413
  also from L have "... = \<Squnion>{x, y, z}" by (simp add: insert_commute)
ballarin@14551
   414
  also from L have "... = x \<squnion> (y \<squnion> z)" by (simp add: join_assoc_lemma)
ballarin@14551
   415
  finally show ?thesis .
ballarin@14551
   416
qed
ballarin@14551
   417
wenzelm@14693
   418
ballarin@14551
   419
subsubsection {* Infimum *}
ballarin@14551
   420
ballarin@14551
   421
lemma (in lattice) meetI:
ballarin@14551
   422
  "[| !!i. greatest L i (Lower L {x, y}) ==> P i;
ballarin@14551
   423
  x \<in> carrier L; y \<in> carrier L |]
ballarin@14551
   424
  ==> P (x \<sqinter> y)"
ballarin@14551
   425
proof (unfold meet_def inf_def)
wenzelm@14693
   426
  assume L: "x \<in> carrier L"  "y \<in> carrier L"
ballarin@14551
   427
    and P: "!!g. greatest L g (Lower L {x, y}) ==> P g"
ballarin@14551
   428
  with inf_of_two_exists obtain i where "greatest L i (Lower L {x, y})" by fast
ballarin@14551
   429
  with L show "P (THE g. greatest L g (Lower L {x, y}))"
ballarin@14551
   430
  by (fast intro: theI2 greatest_unique P)
ballarin@14551
   431
qed
ballarin@14551
   432
ballarin@14551
   433
lemma (in lattice) meet_closed [simp]:
ballarin@14551
   434
  "[| x \<in> carrier L; y \<in> carrier L |] ==> x \<sqinter> y \<in> carrier L"
ballarin@14551
   435
  by (rule meetI) (rule greatest_carrier)
ballarin@14551
   436
wenzelm@14651
   437
lemma (in partial_order) inf_of_singletonI:      (* only reflexivity needed ? *)
ballarin@14551
   438
  "x \<in> carrier L ==> greatest L x (Lower L {x})"
ballarin@14551
   439
  by (rule greatest_LowerI) fast+
ballarin@14551
   440
ballarin@14551
   441
lemma (in partial_order) inf_of_singleton [simp]:
ballarin@19783
   442
  "x \<in> carrier L ==> \<Sqinter> {x} = x"
ballarin@14551
   443
  by (unfold inf_def) (blast intro: greatest_unique greatest_LowerI inf_of_singletonI)
ballarin@14551
   444
ballarin@14551
   445
text {* Condition on A: infimum exists. *}
ballarin@14551
   446
ballarin@14551
   447
lemma (in lattice) inf_insertI:
ballarin@14551
   448
  "[| !!i. greatest L i (Lower L (insert x A)) ==> P i;
ballarin@14551
   449
  greatest L a (Lower L A); x \<in> carrier L; A \<subseteq> carrier L |]
wenzelm@14693
   450
  ==> P (\<Sqinter>(insert x A))"
ballarin@14551
   451
proof (unfold inf_def)
wenzelm@14693
   452
  assume L: "x \<in> carrier L"  "A \<subseteq> carrier L"
ballarin@14551
   453
    and P: "!!g. greatest L g (Lower L (insert x A)) ==> P g"
ballarin@14551
   454
    and greatest_a: "greatest L a (Lower L A)"
ballarin@14551
   455
  from L greatest_a have La: "a \<in> carrier L" by simp
ballarin@14551
   456
  from L inf_of_two_exists greatest_a
ballarin@14551
   457
  obtain i where greatest_i: "greatest L i (Lower L {a, x})" by blast
ballarin@14551
   458
  show "P (THE g. greatest L g (Lower L (insert x A)))"
wenzelm@14693
   459
  proof (rule theI2)
ballarin@14551
   460
    show "greatest L i (Lower L (insert x A))"
ballarin@14551
   461
    proof (rule greatest_LowerI)
ballarin@14551
   462
      fix z
wenzelm@14693
   463
      assume "z \<in> insert x A"
wenzelm@14693
   464
      then show "i \<sqsubseteq> z"
wenzelm@14693
   465
      proof
wenzelm@14693
   466
        assume "z = x" then show ?thesis
wenzelm@14693
   467
          by (simp add: greatest_Lower_above [OF greatest_i] L La)
wenzelm@14693
   468
      next
wenzelm@14693
   469
        assume "z \<in> A"
wenzelm@14693
   470
        with L greatest_i greatest_a show ?thesis
wenzelm@14693
   471
          by (rule_tac trans [where y = a]) (auto dest: greatest_Lower_above)
wenzelm@14693
   472
      qed
wenzelm@14693
   473
    next
wenzelm@14693
   474
      fix y
wenzelm@14693
   475
      assume y: "y \<in> Lower L (insert x A)"
wenzelm@14693
   476
      show "y \<sqsubseteq> i"
wenzelm@14693
   477
      proof (rule greatest_le [OF greatest_i], rule Lower_memI)
wenzelm@14693
   478
	fix z
wenzelm@14693
   479
	assume z: "z \<in> {a, x}"
wenzelm@14693
   480
	then show "y \<sqsubseteq> z"
wenzelm@14693
   481
	proof
wenzelm@14693
   482
          have y': "y \<in> Lower L A"
wenzelm@14693
   483
            apply (rule subsetD [where A = "Lower L (insert x A)"])
wenzelm@14693
   484
            apply (rule Lower_antimono) apply clarify apply assumption
wenzelm@14693
   485
            done
wenzelm@14693
   486
          assume "z = a"
wenzelm@14693
   487
          with y' greatest_a show ?thesis by (fast dest: greatest_le)
wenzelm@14693
   488
	next
wenzelm@14693
   489
          assume "z \<in> {x}"
wenzelm@14693
   490
          with y L show ?thesis by blast
wenzelm@14693
   491
	qed
wenzelm@14693
   492
      qed (rule Lower_closed [THEN subsetD])
wenzelm@14693
   493
    next
wenzelm@14693
   494
      from L show "insert x A \<subseteq> carrier L" by simp
wenzelm@14693
   495
      from greatest_i show "i \<in> carrier L" by simp
ballarin@14551
   496
    qed
ballarin@14551
   497
  next
ballarin@14551
   498
    fix g
ballarin@14551
   499
    assume greatest_g: "greatest L g (Lower L (insert x A))"
ballarin@14551
   500
    show "g = i"
ballarin@14551
   501
    proof (rule greatest_unique)
ballarin@14551
   502
      show "greatest L i (Lower L (insert x A))"
ballarin@14551
   503
      proof (rule greatest_LowerI)
wenzelm@14693
   504
        fix z
wenzelm@14693
   505
        assume "z \<in> insert x A"
wenzelm@14693
   506
        then show "i \<sqsubseteq> z"
wenzelm@14693
   507
	proof
wenzelm@14693
   508
          assume "z = x" then show ?thesis
wenzelm@14693
   509
            by (simp add: greatest_Lower_above [OF greatest_i] L La)
wenzelm@14693
   510
	next
wenzelm@14693
   511
          assume "z \<in> A"
wenzelm@14693
   512
          with L greatest_i greatest_a show ?thesis
wenzelm@14693
   513
            by (rule_tac trans [where y = a]) (auto dest: greatest_Lower_above)
wenzelm@14693
   514
        qed
ballarin@14551
   515
      next
wenzelm@14693
   516
        fix y
wenzelm@14693
   517
        assume y: "y \<in> Lower L (insert x A)"
wenzelm@14693
   518
        show "y \<sqsubseteq> i"
wenzelm@14693
   519
        proof (rule greatest_le [OF greatest_i], rule Lower_memI)
wenzelm@14693
   520
          fix z
wenzelm@14693
   521
          assume z: "z \<in> {a, x}"
wenzelm@14693
   522
          then show "y \<sqsubseteq> z"
wenzelm@14693
   523
          proof
wenzelm@14693
   524
            have y': "y \<in> Lower L A"
wenzelm@14693
   525
	      apply (rule subsetD [where A = "Lower L (insert x A)"])
wenzelm@14693
   526
	      apply (rule Lower_antimono) apply clarify apply assumption
wenzelm@14693
   527
	      done
wenzelm@14693
   528
            assume "z = a"
wenzelm@14693
   529
            with y' greatest_a show ?thesis by (fast dest: greatest_le)
wenzelm@14693
   530
	  next
wenzelm@14693
   531
            assume "z \<in> {x}"
wenzelm@14693
   532
            with y L show ?thesis by blast
ballarin@14551
   533
	  qed
wenzelm@14693
   534
        qed (rule Lower_closed [THEN subsetD])
ballarin@14551
   535
      next
wenzelm@14693
   536
        from L show "insert x A \<subseteq> carrier L" by simp
wenzelm@14693
   537
        from greatest_i show "i \<in> carrier L" by simp
ballarin@14551
   538
      qed
ballarin@14551
   539
    qed
ballarin@14551
   540
  qed
ballarin@14551
   541
qed
ballarin@14551
   542
ballarin@14551
   543
lemma (in lattice) finite_inf_greatest:
wenzelm@14693
   544
  "[| finite A; A \<subseteq> carrier L; A ~= {} |] ==> greatest L (\<Sqinter>A) (Lower L A)"
ballarin@14551
   545
proof (induct set: Finites)
ballarin@14551
   546
  case empty then show ?case by simp
ballarin@14551
   547
next
nipkow@15328
   548
  case (insert x A)
ballarin@14551
   549
  show ?case
ballarin@14551
   550
  proof (cases "A = {}")
ballarin@14551
   551
    case True
ballarin@14551
   552
    with insert show ?thesis by (simp add: inf_of_singletonI)
ballarin@14551
   553
  next
ballarin@14551
   554
    case False
ballarin@14551
   555
    from insert show ?thesis
ballarin@14551
   556
    proof (rule_tac inf_insertI)
wenzelm@14693
   557
      from False insert show "greatest L (\<Sqinter>A) (Lower L A)" by simp
ballarin@14551
   558
    qed simp_all
ballarin@14551
   559
  qed
ballarin@14551
   560
qed
ballarin@14551
   561
ballarin@14551
   562
lemma (in lattice) finite_inf_insertI:
ballarin@14551
   563
  assumes P: "!!i. greatest L i (Lower L (insert x A)) ==> P i"
wenzelm@14693
   564
    and xA: "finite A"  "x \<in> carrier L"  "A \<subseteq> carrier L"
ballarin@14551
   565
  shows "P (\<Sqinter> (insert x A))"
ballarin@14551
   566
proof (cases "A = {}")
ballarin@14551
   567
  case True with P and xA show ?thesis
ballarin@14551
   568
    by (simp add: inf_of_singletonI)
ballarin@14551
   569
next
ballarin@14551
   570
  case False with P and xA show ?thesis
ballarin@14551
   571
    by (simp add: inf_insertI finite_inf_greatest)
ballarin@14551
   572
qed
ballarin@14551
   573
ballarin@14551
   574
lemma (in lattice) finite_inf_closed:
wenzelm@14693
   575
  "[| finite A; A \<subseteq> carrier L; A ~= {} |] ==> \<Sqinter>A \<in> carrier L"
ballarin@14551
   576
proof (induct set: Finites)
ballarin@14551
   577
  case empty then show ?case by simp
ballarin@14551
   578
next
nipkow@15328
   579
  case insert then show ?case
ballarin@14551
   580
    by (rule_tac finite_inf_insertI) (simp_all)
ballarin@14551
   581
qed
ballarin@14551
   582
ballarin@14551
   583
lemma (in lattice) meet_left:
ballarin@14551
   584
  "[| x \<in> carrier L; y \<in> carrier L |] ==> x \<sqinter> y \<sqsubseteq> x"
wenzelm@14693
   585
  by (rule meetI [folded meet_def]) (blast dest: greatest_mem)
ballarin@14551
   586
ballarin@14551
   587
lemma (in lattice) meet_right:
ballarin@14551
   588
  "[| x \<in> carrier L; y \<in> carrier L |] ==> x \<sqinter> y \<sqsubseteq> y"
wenzelm@14693
   589
  by (rule meetI [folded meet_def]) (blast dest: greatest_mem)
ballarin@14551
   590
ballarin@14551
   591
lemma (in lattice) inf_of_two_greatest:
ballarin@14551
   592
  "[| x \<in> carrier L; y \<in> carrier L |] ==>
ballarin@14551
   593
  greatest L (\<Sqinter> {x, y}) (Lower L {x, y})"
ballarin@14551
   594
proof (unfold inf_def)
wenzelm@14693
   595
  assume L: "x \<in> carrier L"  "y \<in> carrier L"
ballarin@14551
   596
  with inf_of_two_exists obtain s where "greatest L s (Lower L {x, y})" by fast
ballarin@14551
   597
  with L
ballarin@14551
   598
  show "greatest L (THE xa. greatest L xa (Lower L {x, y})) (Lower L {x, y})"
ballarin@14551
   599
  by (fast intro: theI2 greatest_unique)  (* blast fails *)
ballarin@14551
   600
qed
ballarin@14551
   601
ballarin@14551
   602
lemma (in lattice) meet_le:
wenzelm@14693
   603
  assumes sub: "z \<sqsubseteq> x"  "z \<sqsubseteq> y"
wenzelm@14693
   604
    and L: "x \<in> carrier L"  "y \<in> carrier L"  "z \<in> carrier L"
ballarin@14551
   605
  shows "z \<sqsubseteq> x \<sqinter> y"
ballarin@14551
   606
proof (rule meetI)
ballarin@14551
   607
  fix i
ballarin@14551
   608
  assume "greatest L i (Lower L {x, y})"
ballarin@14551
   609
  with sub L show "z \<sqsubseteq> i" by (fast elim: greatest_le intro: Lower_memI)
ballarin@14551
   610
qed
wenzelm@14693
   611
ballarin@14551
   612
lemma (in lattice) meet_assoc_lemma:
wenzelm@14693
   613
  assumes L: "x \<in> carrier L"  "y \<in> carrier L"  "z \<in> carrier L"
wenzelm@14693
   614
  shows "x \<sqinter> (y \<sqinter> z) = \<Sqinter>{x, y, z}"
ballarin@14551
   615
proof (rule finite_inf_insertI)
ballarin@14551
   616
  txt {* The textbook argument in Jacobson I, p 457 *}
ballarin@14551
   617
  fix i
ballarin@14551
   618
  assume inf: "greatest L i (Lower L {x, y, z})"
ballarin@14551
   619
  show "x \<sqinter> (y \<sqinter> z) = i"
ballarin@14551
   620
  proof (rule anti_sym)
ballarin@14551
   621
    from inf L show "i \<sqsubseteq> x \<sqinter> (y \<sqinter> z)"
ballarin@14551
   622
      by (fastsimp intro!: meet_le elim: greatest_Lower_above)
ballarin@14551
   623
  next
ballarin@14551
   624
    from inf L show "x \<sqinter> (y \<sqinter> z) \<sqsubseteq> i"
ballarin@14551
   625
    by (erule_tac greatest_le)
ballarin@14551
   626
      (blast intro!: Lower_memI intro: trans meet_left meet_right meet_closed)
ballarin@14551
   627
  qed (simp_all add: L greatest_carrier [OF inf])
ballarin@14551
   628
qed (simp_all add: L)
ballarin@14551
   629
ballarin@14551
   630
lemma meet_comm:
ballarin@19783
   631
  fixes L (structure)
ballarin@14551
   632
  shows "x \<sqinter> y = y \<sqinter> x"
ballarin@14551
   633
  by (unfold meet_def) (simp add: insert_commute)
ballarin@14551
   634
ballarin@14551
   635
lemma (in lattice) meet_assoc:
wenzelm@14693
   636
  assumes L: "x \<in> carrier L"  "y \<in> carrier L"  "z \<in> carrier L"
ballarin@14551
   637
  shows "(x \<sqinter> y) \<sqinter> z = x \<sqinter> (y \<sqinter> z)"
ballarin@14551
   638
proof -
ballarin@14551
   639
  have "(x \<sqinter> y) \<sqinter> z = z \<sqinter> (x \<sqinter> y)" by (simp only: meet_comm)
ballarin@14551
   640
  also from L have "... = \<Sqinter> {z, x, y}" by (simp add: meet_assoc_lemma)
ballarin@14551
   641
  also from L have "... = \<Sqinter> {x, y, z}" by (simp add: insert_commute)
ballarin@14551
   642
  also from L have "... = x \<sqinter> (y \<sqinter> z)" by (simp add: meet_assoc_lemma)
ballarin@14551
   643
  finally show ?thesis .
ballarin@14551
   644
qed
ballarin@14551
   645
wenzelm@14693
   646
ballarin@14551
   647
subsection {* Total Orders *}
ballarin@14551
   648
ballarin@14551
   649
locale total_order = lattice +
ballarin@14551
   650
  assumes total: "[| x \<in> carrier L; y \<in> carrier L |] ==> x \<sqsubseteq> y | y \<sqsubseteq> x"
ballarin@14551
   651
ballarin@14551
   652
text {* Introduction rule: the usual definition of total order *}
ballarin@14551
   653
ballarin@14551
   654
lemma (in partial_order) total_orderI:
ballarin@14551
   655
  assumes total: "!!x y. [| x \<in> carrier L; y \<in> carrier L |] ==> x \<sqsubseteq> y | y \<sqsubseteq> x"
ballarin@14551
   656
  shows "total_order L"
ballarin@19984
   657
proof intro_locales
ballarin@14551
   658
  show "lattice_axioms L"
ballarin@14551
   659
  proof (rule lattice_axioms.intro)
ballarin@14551
   660
    fix x y
wenzelm@14693
   661
    assume L: "x \<in> carrier L"  "y \<in> carrier L"
ballarin@14551
   662
    show "EX s. least L s (Upper L {x, y})"
ballarin@14551
   663
    proof -
ballarin@14551
   664
      note total L
ballarin@14551
   665
      moreover
ballarin@14551
   666
      {
wenzelm@14693
   667
        assume "x \<sqsubseteq> y"
ballarin@14551
   668
        with L have "least L y (Upper L {x, y})"
wenzelm@14693
   669
          by (rule_tac least_UpperI) auto
ballarin@14551
   670
      }
ballarin@14551
   671
      moreover
ballarin@14551
   672
      {
wenzelm@14693
   673
        assume "y \<sqsubseteq> x"
ballarin@14551
   674
        with L have "least L x (Upper L {x, y})"
wenzelm@14693
   675
          by (rule_tac least_UpperI) auto
ballarin@14551
   676
      }
ballarin@14551
   677
      ultimately show ?thesis by blast
ballarin@14551
   678
    qed
ballarin@14551
   679
  next
ballarin@14551
   680
    fix x y
wenzelm@14693
   681
    assume L: "x \<in> carrier L"  "y \<in> carrier L"
ballarin@14551
   682
    show "EX i. greatest L i (Lower L {x, y})"
ballarin@14551
   683
    proof -
ballarin@14551
   684
      note total L
ballarin@14551
   685
      moreover
ballarin@14551
   686
      {
wenzelm@14693
   687
        assume "y \<sqsubseteq> x"
ballarin@14551
   688
        with L have "greatest L y (Lower L {x, y})"
wenzelm@14693
   689
          by (rule_tac greatest_LowerI) auto
ballarin@14551
   690
      }
ballarin@14551
   691
      moreover
ballarin@14551
   692
      {
wenzelm@14693
   693
        assume "x \<sqsubseteq> y"
ballarin@14551
   694
        with L have "greatest L x (Lower L {x, y})"
wenzelm@14693
   695
          by (rule_tac greatest_LowerI) auto
ballarin@14551
   696
      }
ballarin@14551
   697
      ultimately show ?thesis by blast
ballarin@14551
   698
    qed
ballarin@14551
   699
  qed
ballarin@14551
   700
qed (assumption | rule total_order_axioms.intro)+
ballarin@14551
   701
wenzelm@14693
   702
ballarin@14551
   703
subsection {* Complete lattices *}
ballarin@14551
   704
ballarin@14551
   705
locale complete_lattice = lattice +
ballarin@14551
   706
  assumes sup_exists:
ballarin@14551
   707
    "[| A \<subseteq> carrier L |] ==> EX s. least L s (Upper L A)"
ballarin@14551
   708
    and inf_exists:
ballarin@14551
   709
    "[| A \<subseteq> carrier L |] ==> EX i. greatest L i (Lower L A)"
ballarin@14551
   710
ballarin@14551
   711
text {* Introduction rule: the usual definition of complete lattice *}
ballarin@14551
   712
ballarin@14551
   713
lemma (in partial_order) complete_latticeI:
ballarin@14551
   714
  assumes sup_exists:
ballarin@14551
   715
    "!!A. [| A \<subseteq> carrier L |] ==> EX s. least L s (Upper L A)"
ballarin@14551
   716
    and inf_exists:
ballarin@14551
   717
    "!!A. [| A \<subseteq> carrier L |] ==> EX i. greatest L i (Lower L A)"
ballarin@14551
   718
  shows "complete_lattice L"
ballarin@19984
   719
proof intro_locales
ballarin@14551
   720
  show "lattice_axioms L"
wenzelm@14693
   721
    by (rule lattice_axioms.intro) (blast intro: sup_exists inf_exists)+
ballarin@14551
   722
qed (assumption | rule complete_lattice_axioms.intro)+
ballarin@14551
   723
wenzelm@14651
   724
constdefs (structure L)
wenzelm@14651
   725
  top :: "_ => 'a" ("\<top>\<index>")
wenzelm@14651
   726
  "\<top> == sup L (carrier L)"
ballarin@14551
   727
wenzelm@14651
   728
  bottom :: "_ => 'a" ("\<bottom>\<index>")
wenzelm@14651
   729
  "\<bottom> == inf L (carrier L)"
ballarin@14551
   730
ballarin@14551
   731
ballarin@14551
   732
lemma (in complete_lattice) supI:
ballarin@14551
   733
  "[| !!l. least L l (Upper L A) ==> P l; A \<subseteq> carrier L |]
wenzelm@14651
   734
  ==> P (\<Squnion>A)"
ballarin@14551
   735
proof (unfold sup_def)
ballarin@14551
   736
  assume L: "A \<subseteq> carrier L"
ballarin@14551
   737
    and P: "!!l. least L l (Upper L A) ==> P l"
ballarin@14551
   738
  with sup_exists obtain s where "least L s (Upper L A)" by blast
ballarin@14551
   739
  with L show "P (THE l. least L l (Upper L A))"
ballarin@14551
   740
  by (fast intro: theI2 least_unique P)
ballarin@14551
   741
qed
ballarin@14551
   742
ballarin@14551
   743
lemma (in complete_lattice) sup_closed [simp]:
wenzelm@14693
   744
  "A \<subseteq> carrier L ==> \<Squnion>A \<in> carrier L"
ballarin@14551
   745
  by (rule supI) simp_all
ballarin@14551
   746
ballarin@14551
   747
lemma (in complete_lattice) top_closed [simp, intro]:
ballarin@14551
   748
  "\<top> \<in> carrier L"
ballarin@14551
   749
  by (unfold top_def) simp
ballarin@14551
   750
ballarin@14551
   751
lemma (in complete_lattice) infI:
ballarin@14551
   752
  "[| !!i. greatest L i (Lower L A) ==> P i; A \<subseteq> carrier L |]
wenzelm@14693
   753
  ==> P (\<Sqinter>A)"
ballarin@14551
   754
proof (unfold inf_def)
ballarin@14551
   755
  assume L: "A \<subseteq> carrier L"
ballarin@14551
   756
    and P: "!!l. greatest L l (Lower L A) ==> P l"
ballarin@14551
   757
  with inf_exists obtain s where "greatest L s (Lower L A)" by blast
ballarin@14551
   758
  with L show "P (THE l. greatest L l (Lower L A))"
ballarin@14551
   759
  by (fast intro: theI2 greatest_unique P)
ballarin@14551
   760
qed
ballarin@14551
   761
ballarin@14551
   762
lemma (in complete_lattice) inf_closed [simp]:
wenzelm@14693
   763
  "A \<subseteq> carrier L ==> \<Sqinter>A \<in> carrier L"
ballarin@14551
   764
  by (rule infI) simp_all
ballarin@14551
   765
ballarin@14551
   766
lemma (in complete_lattice) bottom_closed [simp, intro]:
ballarin@14551
   767
  "\<bottom> \<in> carrier L"
ballarin@14551
   768
  by (unfold bottom_def) simp
ballarin@14551
   769
ballarin@14551
   770
text {* Jacobson: Theorem 8.1 *}
ballarin@14551
   771
ballarin@14551
   772
lemma Lower_empty [simp]:
ballarin@14551
   773
  "Lower L {} = carrier L"
ballarin@14551
   774
  by (unfold Lower_def) simp
ballarin@14551
   775
ballarin@14551
   776
lemma Upper_empty [simp]:
ballarin@14551
   777
  "Upper L {} = carrier L"
ballarin@14551
   778
  by (unfold Upper_def) simp
ballarin@14551
   779
ballarin@14551
   780
theorem (in partial_order) complete_lattice_criterion1:
ballarin@14551
   781
  assumes top_exists: "EX g. greatest L g (carrier L)"
ballarin@14551
   782
    and inf_exists:
ballarin@14551
   783
      "!!A. [| A \<subseteq> carrier L; A ~= {} |] ==> EX i. greatest L i (Lower L A)"
ballarin@14551
   784
  shows "complete_lattice L"
ballarin@14551
   785
proof (rule complete_latticeI)
ballarin@14551
   786
  from top_exists obtain top where top: "greatest L top (carrier L)" ..
ballarin@14551
   787
  fix A
ballarin@14551
   788
  assume L: "A \<subseteq> carrier L"
ballarin@14551
   789
  let ?B = "Upper L A"
ballarin@14551
   790
  from L top have "top \<in> ?B" by (fast intro!: Upper_memI intro: greatest_le)
ballarin@14551
   791
  then have B_non_empty: "?B ~= {}" by fast
ballarin@14551
   792
  have B_L: "?B \<subseteq> carrier L" by simp
ballarin@14551
   793
  from inf_exists [OF B_L B_non_empty]
ballarin@14551
   794
  obtain b where b_inf_B: "greatest L b (Lower L ?B)" ..
ballarin@14551
   795
  have "least L b (Upper L A)"
ballarin@14551
   796
apply (rule least_UpperI)
wenzelm@14693
   797
   apply (rule greatest_le [where A = "Lower L ?B"])
ballarin@14551
   798
    apply (rule b_inf_B)
ballarin@14551
   799
   apply (rule Lower_memI)
ballarin@14551
   800
    apply (erule UpperD)
ballarin@14551
   801
     apply assumption
ballarin@14551
   802
    apply (rule L)
ballarin@14551
   803
   apply (fast intro: L [THEN subsetD])
ballarin@14551
   804
  apply (erule greatest_Lower_above [OF b_inf_B])
ballarin@14551
   805
  apply simp
ballarin@14551
   806
 apply (rule L)
ballarin@14551
   807
apply (rule greatest_carrier [OF b_inf_B]) (* rename rule: _closed *)
ballarin@14551
   808
done
ballarin@14551
   809
  then show "EX s. least L s (Upper L A)" ..
ballarin@14551
   810
next
ballarin@14551
   811
  fix A
ballarin@14551
   812
  assume L: "A \<subseteq> carrier L"
ballarin@14551
   813
  show "EX i. greatest L i (Lower L A)"
ballarin@14551
   814
  proof (cases "A = {}")
ballarin@14551
   815
    case True then show ?thesis
ballarin@14551
   816
      by (simp add: top_exists)
ballarin@14551
   817
  next
ballarin@14551
   818
    case False with L show ?thesis
ballarin@14551
   819
      by (rule inf_exists)
ballarin@14551
   820
  qed
ballarin@14551
   821
qed
ballarin@14551
   822
ballarin@14551
   823
(* TODO: prove dual version *)
ballarin@14551
   824
ballarin@14551
   825
subsection {* Examples *}
ballarin@14551
   826
ballarin@14551
   827
subsubsection {* Powerset of a set is a complete lattice *}
ballarin@14551
   828
ballarin@14551
   829
theorem powerset_is_complete_lattice:
ballarin@14551
   830
  "complete_lattice (| carrier = Pow A, le = op \<subseteq> |)"
ballarin@14551
   831
  (is "complete_lattice ?L")
ballarin@14551
   832
proof (rule partial_order.complete_latticeI)
ballarin@14551
   833
  show "partial_order ?L"
ballarin@14551
   834
    by (rule partial_order.intro) auto
ballarin@14551
   835
next
ballarin@14551
   836
  fix B
ballarin@14551
   837
  assume "B \<subseteq> carrier ?L"
ballarin@14551
   838
  then have "least ?L (\<Union> B) (Upper ?L B)"
ballarin@14551
   839
    by (fastsimp intro!: least_UpperI simp: Upper_def)
ballarin@14551
   840
  then show "EX s. least ?L s (Upper ?L B)" ..
ballarin@14551
   841
next
ballarin@14551
   842
  fix B
ballarin@14551
   843
  assume "B \<subseteq> carrier ?L"
ballarin@14551
   844
  then have "greatest ?L (\<Inter> B \<inter> A) (Lower ?L B)"
ballarin@14551
   845
    txt {* @{term "\<Inter> B"} is not the infimum of @{term B}:
ballarin@14551
   846
      @{term "\<Inter> {} = UNIV"} which is in general bigger than @{term "A"}! *}
ballarin@14551
   847
    by (fastsimp intro!: greatest_LowerI simp: Lower_def)
ballarin@14551
   848
  then show "EX i. greatest ?L i (Lower ?L B)" ..
ballarin@14551
   849
qed
ballarin@14551
   850
ballarin@14751
   851
text {* An other example, that of the lattice of subgroups of a group,
ballarin@14751
   852
  can be found in Group theory (Section~\ref{sec:subgroup-lattice}). *}
ballarin@14551
   853
wenzelm@14693
   854
end