src/HOL/WF.ML
author paulson
Wed Nov 05 13:23:46 1997 +0100 (1997-11-05)
changeset 4153 e534c4c32d54
parent 4089 96fba19bcbe2
child 4350 1983e4054fd8
permissions -rw-r--r--
Ran expandshort, especially to introduce Safe_tac
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(*  Title:      HOL/wf.ML
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    ID:         $Id$
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    Author:     Tobias Nipkow, with minor changes by Konrad Slind
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    Copyright   1992  University of Cambridge/1995 TU Munich
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Wellfoundedness, induction, and  recursion
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*)
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open WF;
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val H_cong = read_instantiate [("f","H")] (standard(refl RS cong RS cong));
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val H_cong1 = refl RS H_cong;
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(*Restriction to domain A.  If r is well-founded over A then wf(r)*)
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val [prem1,prem2] = goalw WF.thy [wf_def]
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 "[| r <= A Times A;  \
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\    !!x P. [| ! x. (! y. (y,x) : r --> P(y)) --> P(x);  x:A |] ==> P(x) |]  \
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\ ==>  wf(r)";
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by (Clarify_tac 1);
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by (rtac allE 1);
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by (assume_tac 1);
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by (best_tac (claset() addSEs [prem1 RS subsetD RS SigmaE2] addIs [prem2]) 1);
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qed "wfI";
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val major::prems = goalw WF.thy [wf_def]
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    "[| wf(r);          \
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\       !!x.[| ! y. (y,x): r --> P(y) |] ==> P(x) \
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\    |]  ==>  P(a)";
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by (rtac (major RS spec RS mp RS spec) 1);
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by (blast_tac (claset() addIs prems) 1);
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qed "wf_induct";
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(*Perform induction on i, then prove the wf(r) subgoal using prems. *)
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fun wf_ind_tac a prems i = 
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    EVERY [res_inst_tac [("a",a)] wf_induct i,
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           rename_last_tac a ["1"] (i+1),
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           ares_tac prems i];
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val prems = goal WF.thy "[| wf(r);  (a,x):r;  (x,a):r |] ==> P";
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by (subgoal_tac "! x. (a,x):r --> (x,a):r --> P" 1);
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by (blast_tac (claset() addIs prems) 1);
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by (wf_ind_tac "a" prems 1);
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by (Blast_tac 1);
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qed "wf_asym";
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val prems = goal WF.thy "[| wf(r);  (a,a): r |] ==> P";
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by (rtac wf_asym 1);
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by (REPEAT (resolve_tac prems 1));
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qed "wf_irrefl";
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(*transitive closure of a wf relation is wf! *)
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val [prem] = goal WF.thy "wf(r) ==> wf(r^+)";
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by (rewtac wf_def);
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by (Clarify_tac 1);
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(*must retain the universal formula for later use!*)
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by (rtac allE 1 THEN assume_tac 1);
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by (etac mp 1);
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by (res_inst_tac [("a","x")] (prem RS wf_induct) 1);
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by (rtac (impI RS allI) 1);
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by (etac tranclE 1);
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by (Blast_tac 1);
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by (Blast_tac 1);
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qed "wf_trancl";
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(*----------------------------------------------------------------------------
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 * Minimal-element characterization of well-foundedness
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 *---------------------------------------------------------------------------*)
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val wfr::_ = goalw WF.thy [wf_def]
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    "wf r ==> x:Q --> (? z:Q. ! y. (y,z):r --> y~:Q)";
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by (rtac (wfr RS spec RS mp RS spec) 1);
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by (Blast_tac 1);
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val lemma1 = result();
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goalw WF.thy [wf_def]
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    "!!r. (! Q x. x:Q --> (? z:Q. ! y. (y,z):r --> y~:Q)) ==> wf r";
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by (Clarify_tac 1);
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by (dres_inst_tac [("x", "{x. ~ P x}")] spec 1);
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by (Blast_tac 1);
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val lemma2 = result();
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goal WF.thy "wf r = (! Q x. x:Q --> (? z:Q. ! y. (y,z):r --> y~:Q))";
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by (blast_tac (claset() addSIs [lemma1, lemma2]) 1);
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qed "wf_eq_minimal";
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(*---------------------------------------------------------------------------
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 * Wellfoundedness of subsets
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 *---------------------------------------------------------------------------*)
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goal thy "!!r. [| wf(r);  p<=r |] ==> wf(p)";
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by (full_simp_tac (simpset() addsimps [wf_eq_minimal]) 1);
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by (Fast_tac 1);
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qed "wf_subset";
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(*---------------------------------------------------------------------------
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 * Wellfoundedness of the empty relation.
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 *---------------------------------------------------------------------------*)
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goal thy "wf({})";
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by (simp_tac (simpset() addsimps [wf_def]) 1);
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qed "wf_empty";
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AddSIs [wf_empty];
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(*---------------------------------------------------------------------------
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 * Wellfoundedness of `insert'
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 *---------------------------------------------------------------------------*)
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goal WF.thy "wf(insert (y,x) r) = (wf(r) & (x,y) ~: r^*)";
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by (rtac iffI 1);
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 by (blast_tac (claset() addEs [wf_trancl RS wf_irrefl] addIs
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      [rtrancl_into_trancl1,wf_subset,impOfSubs rtrancl_mono]) 1);
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by (asm_full_simp_tac (simpset() addsimps [wf_eq_minimal]) 1);
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by Safe_tac;
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by (EVERY1[rtac allE, atac, etac impE, Blast_tac]);
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by (etac bexE 1);
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by (rename_tac "a" 1);
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by (case_tac "a = x" 1);
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 by (res_inst_tac [("x","a")]bexI 2);
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  by (assume_tac 3);
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 by (Blast_tac 2);
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by (case_tac "y:Q" 1);
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 by (Blast_tac 2);
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by (res_inst_tac [("x","{z. z:Q & (z,y) : r^*}")] allE 1);
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 by (assume_tac 1);
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by (thin_tac "! Q. (? x. x : Q) --> ?P Q" 1);	(*essential for speed*)
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by (blast_tac (claset() addIs [rtrancl_into_rtrancl2]) 1);
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qed "wf_insert";
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AddIffs [wf_insert];
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(*** acyclic ***)
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goalw WF.thy [acyclic_def]
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 "!!r. wf r ==> acyclic r";
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by (blast_tac (claset() addEs [wf_trancl RS wf_irrefl]) 1);
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qed "wf_acyclic";
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goalw WF.thy [acyclic_def]
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  "acyclic(insert (y,x) r) = (acyclic r & (x,y) ~: r^*)";
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by (simp_tac (simpset() addsimps [trancl_insert]) 1);
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by (blast_tac (claset() addEs [make_elim rtrancl_trans]) 1);
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qed "acyclic_insert";
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AddIffs [acyclic_insert];
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goalw WF.thy [acyclic_def] "acyclic(r^-1) = acyclic r";
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by (simp_tac (simpset() addsimps [trancl_inverse]) 1);
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qed "acyclic_inverse";
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(** cut **)
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(*This rewrite rule works upon formulae; thus it requires explicit use of
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  H_cong to expose the equality*)
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goalw WF.thy [cut_def]
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    "(cut f r x = cut g r x) = (!y. (y,x):r --> f(y)=g(y))";
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by (simp_tac (HOL_ss addsimps [expand_fun_eq] addsplits [expand_if]) 1);
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qed "cuts_eq";
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goalw WF.thy [cut_def] "!!x. (x,a):r ==> (cut f r a)(x) = f(x)";
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by (asm_simp_tac HOL_ss 1);
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qed "cut_apply";
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(*** is_recfun ***)
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goalw WF.thy [is_recfun_def,cut_def]
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    "!!f. [| is_recfun r H a f;  ~(b,a):r |] ==> f(b) = arbitrary";
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by (etac ssubst 1);
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by (asm_simp_tac HOL_ss 1);
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qed "is_recfun_undef";
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(*** NOTE! some simplifications need a different finish_tac!! ***)
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fun indhyp_tac hyps =
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    (cut_facts_tac hyps THEN'
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       DEPTH_SOLVE_1 o (ares_tac [TrueI] ORELSE'
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                        eresolve_tac [transD, mp, allE]));
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val wf_super_ss = HOL_ss addSolver indhyp_tac;
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val prems = goalw WF.thy [is_recfun_def,cut_def]
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    "[| wf(r);  trans(r);  is_recfun r H a f;  is_recfun r H b g |] ==> \
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    \ (x,a):r --> (x,b):r --> f(x)=g(x)";
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by (cut_facts_tac prems 1);
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by (etac wf_induct 1);
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by (REPEAT (rtac impI 1 ORELSE etac ssubst 1));
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by (asm_simp_tac (wf_super_ss addcongs [if_cong]) 1);
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qed_spec_mp "is_recfun_equal";
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val prems as [wfr,transr,recfa,recgb,_] = goalw WF.thy [cut_def]
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    "[| wf(r);  trans(r); \
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\       is_recfun r H a f;  is_recfun r H b g;  (b,a):r |] ==> \
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\    cut f r b = g";
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val gundef = recgb RS is_recfun_undef
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and fisg   = recgb RS (recfa RS (transr RS (wfr RS is_recfun_equal)));
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by (cut_facts_tac prems 1);
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by (rtac ext 1);
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by (asm_simp_tac (wf_super_ss addsimps [gundef,fisg]
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                              addsplits [expand_if]) 1);
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qed "is_recfun_cut";
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(*** Main Existence Lemma -- Basic Properties of the_recfun ***)
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val prems = goalw WF.thy [the_recfun_def]
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    "is_recfun r H a f ==> is_recfun r H a (the_recfun r H a)";
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by (res_inst_tac [("P", "is_recfun r H a")] selectI 1);
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by (resolve_tac prems 1);
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qed "is_the_recfun";
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val prems = goal WF.thy
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 "[| wf(r);  trans(r) |] ==> is_recfun r H a (the_recfun r H a)";
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  by (cut_facts_tac prems 1);
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  by (wf_ind_tac "a" prems 1);
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  by (res_inst_tac [("f","cut (%y. H (the_recfun r H y) y) r a1")]
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                   is_the_recfun 1);
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  by (rewtac is_recfun_def);
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  by (stac cuts_eq 1);
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  by (rtac allI 1);
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  by (rtac impI 1);
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  by (res_inst_tac [("f1","H"),("x","y")](arg_cong RS fun_cong) 1);
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  by (subgoal_tac
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         "the_recfun r H y = cut(%x. H(cut(the_recfun r H y) r x) x) r y" 1);
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  by (etac allE 2);
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  by (dtac impE 2);
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  by (atac 2);
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  by (atac 3);
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  by (atac 2);
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  by (etac ssubst 1);
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  by (simp_tac (HOL_ss addsimps [cuts_eq]) 1);
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  by (rtac allI 1);
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  by (rtac impI 1);
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  by (asm_simp_tac (wf_super_ss addsimps[cut_apply,is_recfun_cut,cuts_eq]) 1);
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  by (res_inst_tac [("f1","H"),("x","ya")](arg_cong RS fun_cong) 1);
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  by (fold_tac [is_recfun_def]);
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  by (asm_simp_tac (wf_super_ss addsimps[cut_apply,is_recfun_cut,cuts_eq]) 1);
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qed "unfold_the_recfun";
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val unwind1_the_recfun = rewrite_rule[is_recfun_def] unfold_the_recfun;
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(*--------------Old proof-----------------------------------------------------
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val prems = goal WF.thy
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    "[| wf(r);  trans(r) |] ==> is_recfun r H a (the_recfun r H a)";
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by (cut_facts_tac prems 1);
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by (wf_ind_tac "a" prems 1);
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by (res_inst_tac [("f", "cut (%y. wftrec r H y) r a1")] is_the_recfun 1); 
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by (rewrite_goals_tac [is_recfun_def, wftrec_def]);
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by (stac cuts_eq 1);
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(*Applying the substitution: must keep the quantified assumption!!*)
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by (EVERY1 [Clarify_tac, rtac H_cong1, rtac allE, atac,
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            etac (mp RS ssubst), atac]); 
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by (fold_tac [is_recfun_def]);
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by (asm_simp_tac (wf_super_ss addsimps[cut_apply,is_recfun_cut,cuts_eq]) 1);
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qed "unfold_the_recfun";
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---------------------------------------------------------------------------*)
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(** Removal of the premise trans(r) **)
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val th = rewrite_rule[is_recfun_def]
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                     (trans_trancl RSN (2,(wf_trancl RS unfold_the_recfun)));
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goalw WF.thy [wfrec_def]
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    "!!r. wf(r) ==> wfrec r H a = H (cut (wfrec r H) r a) a";
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by (rtac H_cong 1);
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by (rtac refl 2);
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by (simp_tac (HOL_ss addsimps [cuts_eq]) 1);
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by (rtac allI 1);
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by (rtac impI 1);
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by (simp_tac(HOL_ss addsimps [wfrec_def]) 1);
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by (res_inst_tac [("a1","a")] (th RS ssubst) 1);
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by (atac 1);
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by (forward_tac[wf_trancl] 1);
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by (forward_tac[r_into_trancl] 1);
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by (asm_simp_tac (HOL_ss addsimps [cut_apply]) 1);
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by (rtac H_cong 1);    (*expose the equality of cuts*)
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by (rtac refl 2);
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by (simp_tac (HOL_ss addsimps [cuts_eq, cut_apply, r_into_trancl]) 1);
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by (Clarify_tac 1);
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by (res_inst_tac [("r","r^+")] is_recfun_equal 1);
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by (atac 1);
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by (rtac trans_trancl 1);
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by (rtac unfold_the_recfun 1);
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by (atac 1);
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by (rtac trans_trancl 1);
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by (rtac unfold_the_recfun 1);
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by (atac 1);
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by (rtac trans_trancl 1);
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by (rtac transD 1);
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by (rtac trans_trancl 1);
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by (forw_inst_tac [("a","ya")] r_into_trancl 1);
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by (atac 1);
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by (atac 1);
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by (forw_inst_tac [("a","ya")] r_into_trancl 1);
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by (atac 1);
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qed "wfrec";
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(*--------------Old proof-----------------------------------------------------
clasohm@1475
   293
goalw WF.thy [wfrec_def]
clasohm@1475
   294
    "!!r. wf(r) ==> wfrec r H a = H (cut (wfrec r H) r a) a";
clasohm@923
   295
by (etac (wf_trancl RS wftrec RS ssubst) 1);
clasohm@923
   296
by (rtac trans_trancl 1);
clasohm@923
   297
by (rtac (refl RS H_cong) 1);    (*expose the equality of cuts*)
clasohm@1475
   298
by (simp_tac (HOL_ss addsimps [cuts_eq, cut_apply, r_into_trancl]) 1);
clasohm@923
   299
qed "wfrec";
clasohm@1475
   300
---------------------------------------------------------------------------*)
clasohm@923
   301
clasohm@1475
   302
(*---------------------------------------------------------------------------
clasohm@1475
   303
 * This form avoids giant explosions in proofs.  NOTE USE OF == 
clasohm@1475
   304
 *---------------------------------------------------------------------------*)
clasohm@923
   305
val rew::prems = goal WF.thy
clasohm@1475
   306
    "[| f==wfrec r H;  wf(r) |] ==> f(a) = H (cut f r a) a";
clasohm@923
   307
by (rewtac rew);
clasohm@923
   308
by (REPEAT (resolve_tac (prems@[wfrec]) 1));
clasohm@923
   309
qed "def_wfrec";
clasohm@1475
   310
paulson@3198
   311
paulson@3198
   312
(**** TFL variants ****)
paulson@3198
   313
paulson@3198
   314
goal WF.thy
paulson@3198
   315
    "!R. wf R --> (!P. (!x. (!y. (y,x):R --> P y) --> P x) --> (!x. P x))";
paulson@3708
   316
by (Clarify_tac 1);
paulson@3198
   317
by (res_inst_tac [("r","R"),("P","P"), ("a","x")] wf_induct 1);
paulson@3198
   318
by (assume_tac 1);
paulson@3198
   319
by (Blast_tac 1);
paulson@3198
   320
qed"tfl_wf_induct";
paulson@3198
   321
paulson@3198
   322
goal WF.thy "!f R. (x,a):R --> (cut f R a)(x) = f(x)";
paulson@3708
   323
by (Clarify_tac 1);
paulson@3198
   324
by (rtac cut_apply 1);
paulson@3198
   325
by (assume_tac 1);
paulson@3198
   326
qed"tfl_cut_apply";
paulson@3198
   327
paulson@3198
   328
goal WF.thy "!M R f. (f=wfrec R M) --> wf R --> (!x. f x = M (cut f R x) x)";
paulson@3708
   329
by (Clarify_tac 1);
paulson@4153
   330
by (etac wfrec 1);
paulson@3198
   331
qed "tfl_wfrec";