author  wenzelm 
Wed, 28 Dec 2011 13:00:51 +0100  
changeset 46003  c0fe5e8e4864 
parent 42156  df219e736a5d 
child 47966  b8a94ed1646e 
permissions  rwrr 
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(* Title: CCL/Hered.thy 
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Author: Martin Coen 
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Copyright 1993 University of Cambridge 
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*) 

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header {* Hereditary Termination  cf. Martin Lo\"f *} 
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theory Hered 

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imports Type 

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begin 

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text {* 

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Note that this is based on an untyped equality and so @{text "lam 

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x. b(x)"} is only hereditarily terminating if @{text "ALL x. b(x)"} 

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is. Not so useful for functions! 

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*} 

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definition HTTgen :: "i set => i set" where 
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"HTTgen(R) == 

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{t. t=true  t=false  (EX a b. t= <a, b> & a : R & b : R)  

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(EX f. t = lam x. f(x) & (ALL x. f(x) : R))}" 

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definition HTT :: "i set" 
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where "HTT == gfp(HTTgen)" 

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subsection {* Hereditary Termination *} 

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lemma HTTgen_mono: "mono(%X. HTTgen(X))" 

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apply (unfold HTTgen_def) 

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apply (rule monoI) 

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apply blast 

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done 

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lemma HTTgenXH: 

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"t : HTTgen(A) <> t=true  t=false  (EX a b. t=<a,b> & a : A & b : A)  

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(EX f. t=lam x. f(x) & (ALL x. f(x) : A))" 

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apply (unfold HTTgen_def) 

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apply blast 

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done 

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lemma HTTXH: 

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"t : HTT <> t=true  t=false  (EX a b. t=<a,b> & a : HTT & b : HTT)  

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(EX f. t=lam x. f(x) & (ALL x. f(x) : HTT))" 

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apply (rule HTTgen_mono [THEN HTT_def [THEN def_gfp_Tarski], THEN XHlemma1, unfolded HTTgen_def]) 

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apply blast 

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done 

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subsection {* Introduction Rules for HTT *} 

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lemma HTT_bot: "~ bot : HTT" 

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by (blast dest: HTTXH [THEN iffD1]) 

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lemma HTT_true: "true : HTT" 

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by (blast intro: HTTXH [THEN iffD2]) 

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lemma HTT_false: "false : HTT" 

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by (blast intro: HTTXH [THEN iffD2]) 

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lemma HTT_pair: "<a,b> : HTT <> a : HTT & b : HTT" 

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apply (rule HTTXH [THEN iff_trans]) 

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apply blast 

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done 

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lemma HTT_lam: "lam x. f(x) : HTT <> (ALL x. f(x) : HTT)" 

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apply (rule HTTXH [THEN iff_trans]) 

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apply auto 

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done 

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lemmas HTT_rews1 = HTT_bot HTT_true HTT_false HTT_pair HTT_lam 

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lemma HTT_rews2: 

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"one : HTT" 

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"inl(a) : HTT <> a : HTT" 

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"inr(b) : HTT <> b : HTT" 

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"zero : HTT" 

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"succ(n) : HTT <> n : HTT" 

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"[] : HTT" 

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"x$xs : HTT <> x : HTT & xs : HTT" 

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by (simp_all add: data_defs HTT_rews1) 

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lemmas HTT_rews = HTT_rews1 HTT_rews2 

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subsection {* Coinduction for HTT *} 

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lemma HTT_coinduct: "[ t : R; R <= HTTgen(R) ] ==> t : HTT" 

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apply (erule HTT_def [THEN def_coinduct]) 

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apply assumption 

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done 

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lemma HTT_coinduct3: 

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"[ t : R; R <= HTTgen(lfp(%x. HTTgen(x) Un R Un HTT)) ] ==> t : HTT" 

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apply (erule HTTgen_mono [THEN [3] HTT_def [THEN def_coinduct3]]) 

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apply assumption 

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done 

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lemma HTTgenIs: 
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"true : HTTgen(R)" 
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"false : HTTgen(R)" 
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"[ a : R; b : R ] ==> <a,b> : HTTgen(R)" 
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"!!b. [ !!x. b(x) : R ] ==> lam x. b(x) : HTTgen(R)" 
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"one : HTTgen(R)" 
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"a : lfp(%x. HTTgen(x) Un R Un HTT) ==> inl(a) : HTTgen(lfp(%x. HTTgen(x) Un R Un HTT))" 
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"b : lfp(%x. HTTgen(x) Un R Un HTT) ==> inr(b) : HTTgen(lfp(%x. HTTgen(x) Un R Un HTT))" 
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"zero : HTTgen(lfp(%x. HTTgen(x) Un R Un HTT))" 
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"n : lfp(%x. HTTgen(x) Un R Un HTT) ==> succ(n) : HTTgen(lfp(%x. HTTgen(x) Un R Un HTT))" 
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"[] : HTTgen(lfp(%x. HTTgen(x) Un R Un HTT))" 
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"[ h : lfp(%x. HTTgen(x) Un R Un HTT); t : lfp(%x. HTTgen(x) Un R Un HTT) ] ==> 
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h$t : HTTgen(lfp(%x. HTTgen(x) Un R Un HTT))" 
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unfolding data_defs by (genIs HTTgenXH HTTgen_mono)+ 
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subsection {* Formation Rules for Types *} 

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lemma UnitF: "Unit <= HTT" 

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by (simp add: subsetXH UnitXH HTT_rews) 

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lemma BoolF: "Bool <= HTT" 

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by (fastsimp simp: subsetXH BoolXH iff: HTT_rews) 

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lemma PlusF: "[ A <= HTT; B <= HTT ] ==> A + B <= HTT" 

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by (fastsimp simp: subsetXH PlusXH iff: HTT_rews) 

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lemma SigmaF: "[ A <= HTT; !!x. x:A ==> B(x) <= HTT ] ==> SUM x:A. B(x) <= HTT" 

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by (fastsimp simp: subsetXH SgXH HTT_rews) 

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(*** Formation Rules for Recursive types  using coinduction these only need ***) 

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(*** exhaution rule for typeformer ***) 

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(*Proof by induction  needs induction rule for type*) 

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lemma "Nat <= HTT" 

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apply (simp add: subsetXH) 

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apply clarify 

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apply (erule Nat_ind) 

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apply (fastsimp iff: HTT_rews)+ 

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done 

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lemma NatF: "Nat <= HTT" 

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apply clarify 

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apply (erule HTT_coinduct3) 

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apply (fast intro: HTTgenIs elim!: HTTgen_mono [THEN ci3_RI] dest: NatXH [THEN iffD1]) 

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done 

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lemma ListF: "A <= HTT ==> List(A) <= HTT" 

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apply clarify 

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apply (erule HTT_coinduct3) 

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apply (fast intro!: HTTgenIs elim!: HTTgen_mono [THEN ci3_RI] 

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subsetD [THEN HTTgen_mono [THEN ci3_AI]] 

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dest: ListXH [THEN iffD1]) 

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done 

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lemma ListsF: "A <= HTT ==> Lists(A) <= HTT" 

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apply clarify 

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apply (erule HTT_coinduct3) 

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apply (fast intro!: HTTgenIs elim!: HTTgen_mono [THEN ci3_RI] 

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subsetD [THEN HTTgen_mono [THEN ci3_AI]] dest: ListsXH [THEN iffD1]) 

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done 

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lemma IListsF: "A <= HTT ==> ILists(A) <= HTT" 

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apply clarify 

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apply (erule HTT_coinduct3) 

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apply (fast intro!: HTTgenIs elim!: HTTgen_mono [THEN ci3_RI] 

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subsetD [THEN HTTgen_mono [THEN ci3_AI]] dest: IListsXH [THEN iffD1]) 

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done 

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end 