From 49c323679be0b018a55199295482b6addd6e4cff Mon Sep 17 00:00:00 2001
From: David Aspinall <da@inf.ed.ac.uk>
Date: Mon, 31 Jan 2011 13:21:17 +0000
Subject: Deleted file

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 delete mode 100644 isar/ex/KnasterTarski.thy

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diff --git a/isar/ex/KnasterTarski.thy b/isar/ex/KnasterTarski.thy
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-(********** 
-  This file is copied from Isabelle2009-2. 
- **********)
-
-(*  Title:      HOL/Isar_examples/KnasterTarski.thy
-    Author:     Markus Wenzel, TU Muenchen
-
-Typical textbook proof example.
-*)
-
-header {* Textbook-style reasoning: the Knaster-Tarski Theorem *}
-
-theory KnasterTarski
-imports Main Lattice_Syntax
-begin
-
-
-subsection {* Prose version *}
-
-text {*
-  According to the textbook \cite[pages 93--94]{davey-priestley}, the
-  Knaster-Tarski fixpoint theorem is as follows.\footnote{We have
-  dualized the argument, and tuned the notation a little bit.}
-
-  \textbf{The Knaster-Tarski Fixpoint Theorem.}  Let @{text L} be a
-  complete lattice and @{text "f: L \<rightarrow> L"} an order-preserving map.
-  Then @{text "\<Sqinter>{x \<in> L | f(x) \<le> x}"} is a fixpoint of @{text f}.
-
-  \textbf{Proof.} Let @{text "H = {x \<in> L | f(x) \<le> x}"} and @{text "a =
-  \<Sqinter>H"}.  For all @{text "x \<in> H"} we have @{text "a \<le> x"}, so @{text
-  "f(a) \<le> f(x) \<le> x"}.  Thus @{text "f(a)"} is a lower bound of @{text
-  H}, whence @{text "f(a) \<le> a"}.  We now use this inequality to prove
-  the reverse one (!) and thereby complete the proof that @{text a} is
-  a fixpoint.  Since @{text f} is order-preserving, @{text "f(f(a)) \<le>
-  f(a)"}.  This says @{text "f(a) \<in> H"}, so @{text "a \<le> f(a)"}.
-*}
-
-
-subsection {* Formal versions *}
-
-text {*
-  The Isar proof below closely follows the original presentation.
-  Virtually all of the prose narration has been rephrased in terms of
-  formal Isar language elements.  Just as many textbook-style proofs,
-  there is a strong bias towards forward proof, and several bends in
-  the course of reasoning.
-*}
-
-theorem Knaster_Tarski:
-  fixes f :: "'a::complete_lattice \<Rightarrow> 'a"
-  assumes "mono f"
-  shows "\<exists>a. f a = a"
-proof
-  let ?H = "{u. f u \<le> u}"
-  let ?a = "\<Sqinter>?H"
-  show "f ?a = ?a"
-  proof -
-    {
-      fix x
-      assume "x \<in> ?H"
-      then have "?a \<le> x" by (rule Inf_lower)
-      with `mono f` have "f ?a \<le> f x" ..
-      also from `x \<in> ?H` have "\<dots> \<le> x" ..
-      finally have "f ?a \<le> x" .
-    }
-    then have "f ?a \<le> ?a" by (rule Inf_greatest)
-    {
-      also presume "\<dots> \<le> f ?a"
-      finally (order_antisym) show ?thesis .
-    }
-    from `mono f` and `f ?a \<le> ?a` have "f (f ?a) \<le> f ?a" ..
-    then have "f ?a \<in> ?H" ..
-    then show "?a \<le> f ?a" by (rule Inf_lower)
-  qed
-qed
-
-text {*
-  Above we have used several advanced Isar language elements, such as
-  explicit block structure and weak assumptions.  Thus we have
-  mimicked the particular way of reasoning of the original text.
-
-  In the subsequent version the order of reasoning is changed to
-  achieve structured top-down decomposition of the problem at the
-  outer level, while only the inner steps of reasoning are done in a
-  forward manner.  We are certainly more at ease here, requiring only
-  the most basic features of the Isar language.
-*}
-
-theorem Knaster_Tarski':
-  fixes f :: "'a::complete_lattice \<Rightarrow> 'a"
-  assumes "mono f"
-  shows "\<exists>a. f a = a"
-proof
-  let ?H = "{u. f u \<le> u}"
-  let ?a = "\<Sqinter>?H"
-  show "f ?a = ?a"
-  proof (rule order_antisym)
-    show "f ?a \<le> ?a"
-    proof (rule Inf_greatest)
-      fix x
-      assume "x \<in> ?H"
-      then have "?a \<le> x" by (rule Inf_lower)
-      with `mono f` have "f ?a \<le> f x" ..
-      also from `x \<in> ?H` have "\<dots> \<le> x" ..
-      finally show "f ?a \<le> x" .
-    qed
-    show "?a \<le> f ?a"
-    proof (rule Inf_lower)
-      from `mono f` and `f ?a \<le> ?a` have "f (f ?a) \<le> f ?a" ..
-      then show "f ?a \<in> ?H" ..
-    qed
-  qed
-qed
-
-end
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