src/LCF/ex/Ex1.thy
author blanchet
Mon, 15 Sep 2014 10:49:07 +0200
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header {*  Section 10.4 *}
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theory Ex1
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imports LCF
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begin
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axiomatization
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  P     :: "'a => tr" and
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  G     :: "'a => 'a" and
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  H     :: "'a => 'a" and
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  K     :: "('a => 'a) => ('a => 'a)"
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where
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  P_strict:     "P(UU) = UU" and
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  K:            "K = (%h x. P(x) => x | h(h(G(x))))" and
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  H:            "H = FIX(K)"
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declare P_strict [simp] K [simp]
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lemma H_unfold: "H = K(H)"
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  apply (simplesubst H)
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  apply (rule FIX_eq [symmetric])
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  done
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lemma H_strict [simp]: "H(UU)=UU"
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  apply (simplesubst H_unfold)
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  apply simp
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  done
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lemma H_idemp_lemma: "ALL x. H(FIX(K,x)) = FIX(K,x)"
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  apply (tactic {* induct_tac @{context} "K" 1 *})
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  apply simp
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  apply (simp split: COND_cases_iff)
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  apply (intro strip)
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  apply (subst H_unfold)
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  apply simp
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  done
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lemma H_idemp: "ALL x. H(H(x)) = H(x)"
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  apply (rule H_idemp_lemma [folded H])
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  done
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end