src/ZF/WF.ML
changeset 0 a5a9c433f639
child 6 8ce8c4d13d4d
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/ZF/WF.ML	Thu Sep 16 12:20:38 1993 +0200
@@ -0,0 +1,262 @@
+(*  Title: 	ZF/wf.ML
+    ID:         $Id$
+    Author: 	Tobias Nipkow and Lawrence C Paulson
+    Copyright   1992  University of Cambridge
+
+For wf.thy.  Well-founded Recursion
+
+Derived first for transitive relations, and finally for arbitrary WF relations
+via wf_trancl and trans_trancl.
+
+It is difficult to derive this general case directly, using r^+ instead of
+r.  In is_recfun, the two occurrences of the relation must have the same
+form.  Inserting r^+ in the_recfun or wftrec yields a recursion rule with
+r^+ -`` {a} instead of r-``{a}.  This recursion rule is stronger in
+principle, but harder to use, especially to prove wfrec_eclose_eq in
+epsilon.ML.  Expanding out the definition of wftrec in wfrec would yield
+a mess.
+*)
+
+open WF;
+
+val [H_cong] = mk_typed_congs WF.thy[("H","[i,i]=>i")];
+
+val wf_ss = ZF_ss addcongs [H_cong];
+
+
+(*** Well-founded relations ***)
+
+(*Are these two theorems at all useful??*)
+
+(*If every subset of field(r) possesses an r-minimal element then wf(r).
+  Seems impossible to prove this for domain(r) or range(r) instead...
+  Consider in particular finite wf relations!*)
+val [prem1,prem2] = goalw WF.thy [wf_def]
+    "[| field(r)<=A;  \
+\       !!Z u. [| Z<=A;  u:Z;  ALL x:Z. EX y:Z. <y,x>:r |] ==> False |] \
+\    ==>  wf(r)";
+by (rtac (equals0I RS disjCI RS allI) 1);
+by (rtac prem2 1);
+by (res_inst_tac [ ("B1", "Z") ] (prem1 RS (Int_lower1 RS subset_trans)) 1);
+by (fast_tac ZF_cs 1);
+by (fast_tac ZF_cs 1);
+val wfI = result();
+
+(*If r allows well-founded induction then wf(r)*)
+val [prem1,prem2] = goal WF.thy
+    "[| field(r)<=A;  \
+\       !!B. ALL x:A. (ALL y. <y,x>: r --> y:B) --> x:B ==> A<=B |]  \
+\    ==>  wf(r)";
+by (rtac (prem1 RS wfI) 1);
+by (res_inst_tac [ ("B", "A-Z") ] (prem2 RS subsetCE) 1);
+by (fast_tac ZF_cs 3);
+by (fast_tac ZF_cs 2);
+by (fast_tac ZF_cs 1);
+val wfI2 = result();
+
+
+(** Well-founded Induction **)
+
+(*Consider the least z in domain(r) Un {a} such that P(z) does not hold...*)
+val major::prems = goalw WF.thy [wf_def]
+    "[| wf(r);          \
+\       !!x.[| ALL y. <y,x>: r --> P(y) |] ==> P(x) \
+\    |]  ==>  P(a)";
+by (res_inst_tac [ ("x", "{z:domain(r) Un {a}. ~P(z)}") ]  (major RS allE) 1);
+by (etac disjE 1);
+by (rtac classical 1);
+by (etac equals0D 1);
+by (etac (singletonI RS UnI2 RS CollectI) 1);
+by (etac bexE 1);
+by (etac CollectE 1);
+by (etac swap 1);
+by (resolve_tac prems 1);
+by (fast_tac ZF_cs 1);
+val wf_induct = result();
+
+(*Perform induction on i, then prove the wf(r) subgoal using prems. *)
+fun wf_ind_tac a prems i = 
+    EVERY [res_inst_tac [("a",a)] wf_induct i,
+	   rename_last_tac a ["1"] (i+1),
+	   ares_tac prems i];
+
+(*The form of this rule is designed to match wfI2*)
+val wfr::amem::prems = goal WF.thy
+    "[| wf(r);  a:A;  field(r)<=A;  \
+\       !!x.[| x: A;  ALL y. <y,x>: r --> P(y) |] ==> P(x) \
+\    |]  ==>  P(a)";
+by (rtac (amem RS rev_mp) 1);
+by (wf_ind_tac "a" [wfr] 1);
+by (rtac impI 1);
+by (eresolve_tac prems 1);
+by (fast_tac (ZF_cs addIs (prems RL [subsetD])) 1);
+val wf_induct2 = result();
+
+val prems = goal WF.thy "[| wf(r);  <a,x>:r;  <x,a>:r |] ==> False";
+by (subgoal_tac "ALL x. <a,x>:r --> <x,a>:r --> False" 1);
+by (wf_ind_tac "a" prems 2);
+by (fast_tac ZF_cs 2);
+by (fast_tac (FOL_cs addIs prems) 1);
+val wf_anti_sym = result();
+
+(*transitive closure of a WF relation is WF!*)
+val [prem] = goal WF.thy "wf(r) ==> wf(r^+)";
+by (rtac (trancl_type RS field_rel_subset RS wfI2) 1);
+by (rtac subsetI 1);
+(*must retain the universal formula for later use!*)
+by (rtac (bspec RS mp) 1 THEN assume_tac 1 THEN assume_tac 1);
+by (eres_inst_tac [("a","x")] (prem RS wf_induct2) 1);
+by (rtac subset_refl 1);
+by (rtac (impI RS allI) 1);
+by (etac tranclE 1);
+by (etac (bspec RS mp) 1);
+by (etac fieldI1 1);
+by (fast_tac ZF_cs 1);
+by (fast_tac ZF_cs 1);
+val wf_trancl = result();
+
+(** r-``{a} is the set of everything under a in r **)
+
+val underI = standard (vimage_singleton_iff RS iffD2);
+val underD = standard (vimage_singleton_iff RS iffD1);
+
+(** is_recfun **)
+
+val [major] = goalw WF.thy [is_recfun_def]
+    "is_recfun(r,a,H,f) ==> f: r-``{a} -> range(f)";
+by (rtac (major RS ssubst) 1);
+by (rtac (lamI RS rangeI RS lam_type) 1);
+by (assume_tac 1);
+val is_recfun_type = result();
+
+val [isrec,rel] = goalw WF.thy [is_recfun_def]
+    "[| is_recfun(r,a,H,f); <x,a>:r |] ==> f`x = H(x, restrict(f,r-``{x}))";
+by (res_inst_tac [("P", "%x.?t(x) = ?u::i")] (isrec RS ssubst) 1);
+by (rtac (rel RS underI RS beta) 1);
+val apply_recfun = result();
+
+(*eresolve_tac transD solves <a,b>:r using transitivity AT MOST ONCE
+  spec RS mp  instantiates induction hypotheses*)
+fun indhyp_tac hyps =
+    ares_tac (TrueI::hyps) ORELSE' 
+    (cut_facts_tac hyps THEN'
+       DEPTH_SOLVE_1 o (ares_tac [TrueI, ballI] ORELSE'
+		        eresolve_tac [underD, transD, spec RS mp]));
+
+(*** NOTE! some simplifications need a different auto_tac!! ***)
+val wf_super_ss = wf_ss setauto indhyp_tac;
+
+val prems = goalw WF.thy [is_recfun_def]
+    "[| wf(r);  trans(r);  is_recfun(r,a,H,f);  is_recfun(r,b,H,g) |] ==> \
+\    <x,a>:r --> <x,b>:r --> f`x=g`x";
+by (cut_facts_tac prems 1);
+by (wf_ind_tac "x" prems 1);
+by (REPEAT (rtac impI 1 ORELSE etac ssubst 1));
+by (rewtac restrict_def);
+by (ASM_SIMP_TAC (wf_super_ss addrews [vimage_singleton_iff]) 1);
+val is_recfun_equal_lemma = result();
+val is_recfun_equal = standard (is_recfun_equal_lemma RS mp RS mp);
+
+val prems as [wfr,transr,recf,recg,_] = goal WF.thy
+    "[| wf(r);  trans(r);       \
+\       is_recfun(r,a,H,f);  is_recfun(r,b,H,g);  <b,a>:r |] ==> \
+\    restrict(f, r-``{b}) = g";
+by (cut_facts_tac prems 1);
+by (rtac (consI1 RS restrict_type RS fun_extension) 1);
+by (etac is_recfun_type 1);
+by (ALLGOALS
+    (ASM_SIMP_TAC (wf_super_ss addrews
+		   [ [wfr,transr,recf,recg] MRS is_recfun_equal ])));
+val is_recfun_cut = result();
+
+(*** Main Existence Lemma ***)
+
+val prems = goal WF.thy
+    "[| wf(r); trans(r); is_recfun(r,a,H,f); is_recfun(r,a,H,g) |]  ==>  f=g";
+by (cut_facts_tac prems 1);
+by (rtac fun_extension 1);
+by (REPEAT (ares_tac [is_recfun_equal] 1
+     ORELSE eresolve_tac [is_recfun_type,underD] 1));
+val is_recfun_functional = result();
+
+(*If some f satisfies is_recfun(r,a,H,-) then so does the_recfun(r,a,H) *)
+val prems = goalw WF.thy [the_recfun_def]
+    "[| is_recfun(r,a,H,f);  wf(r);  trans(r) |]  \
+\    ==> is_recfun(r, a, H, the_recfun(r,a,H))";
+by (rtac (ex1I RS theI) 1);
+by (REPEAT (ares_tac (prems@[is_recfun_functional]) 1));
+val is_the_recfun = result();
+
+val prems = goal WF.thy
+    "[| wf(r);  trans(r) |] ==> is_recfun(r, a, H, the_recfun(r,a,H))";
+by (cut_facts_tac prems 1);
+by (wf_ind_tac "a" prems 1);
+by (res_inst_tac [("f", "lam y: r-``{a1}. wftrec(r,y,H)")] is_the_recfun 1);
+by (REPEAT (assume_tac 2));
+by (rewrite_goals_tac [is_recfun_def, wftrec_def]);
+(*Applying the substitution: must keep the quantified assumption!!*)
+by (REPEAT (dtac underD 1 ORELSE resolve_tac [refl, lam_cong, H_cong] 1));
+by (fold_tac [is_recfun_def]);
+by (rtac (consI1 RS restrict_type RSN (2,fun_extension)) 1);
+by (rtac is_recfun_type 1);
+by (ALLGOALS
+    (ASM_SIMP_TAC
+     (wf_super_ss addrews [underI RS beta, apply_recfun, is_recfun_cut])));
+val unfold_the_recfun = result();
+
+
+(*** Unfolding wftrec ***)
+
+val prems = goal WF.thy
+    "[| wf(r);  trans(r);  <b,a>:r |] ==> \
+\    restrict(the_recfun(r,a,H), r-``{b}) = the_recfun(r,b,H)";
+by (REPEAT (ares_tac (prems @ [is_recfun_cut, unfold_the_recfun]) 1));
+val the_recfun_cut = result();
+
+(*NOT SUITABLE FOR REWRITING since it is recursive!*)
+val prems = goalw WF.thy [wftrec_def]
+    "[| wf(r);  trans(r) |] ==> \
+\    wftrec(r,a,H) = H(a, lam x: r-``{a}. wftrec(r,x,H))";
+by (rtac (rewrite_rule [is_recfun_def] unfold_the_recfun RS ssubst) 1);
+by (ALLGOALS (ASM_SIMP_TAC
+	      (wf_ss addrews (prems@[vimage_singleton_iff RS iff_sym, 
+				     the_recfun_cut]))));
+val wftrec = result();
+
+(** Removal of the premise trans(r) **)
+
+(*NOT SUITABLE FOR REWRITING since it is recursive!*)
+val [wfr] = goalw WF.thy [wfrec_def]
+    "wf(r) ==> wfrec(r,a,H) = H(a, lam x:r-``{a}. wfrec(r,x,H))";
+by (rtac (wfr RS wf_trancl RS wftrec RS ssubst) 1);
+by (rtac trans_trancl 1);
+by (rtac (refl RS H_cong) 1);
+by (rtac (vimage_pair_mono RS restrict_lam_eq) 1);
+by (etac r_into_trancl 1);
+by (rtac subset_refl 1);
+val wfrec = result();
+
+(*This form avoids giant explosions in proofs.  NOTE USE OF == *)
+val rew::prems = goal WF.thy
+    "[| !!x. h(x)==wfrec(r,x,H);  wf(r) |] ==> \
+\    h(a) = H(a, lam x: r-``{a}. h(x))";
+by (rewtac rew);
+by (REPEAT (resolve_tac (prems@[wfrec]) 1));
+val def_wfrec = result();
+
+val prems = goal WF.thy
+    "[| wf(r);  a:A;  field(r)<=A;  \
+\       !!x u. [| x: A;  u: Pi(r-``{x}, B) |] ==> H(x,u) : B(x)   \
+\    |] ==> wfrec(r,a,H) : B(a)";
+by (res_inst_tac [("a","a")] wf_induct2 1);
+by (rtac (wfrec RS ssubst) 4);
+by (REPEAT (ares_tac (prems@[lam_type]) 1
+     ORELSE eresolve_tac [spec RS mp, underD] 1));
+val wfrec_type = result();
+
+val prems = goalw WF.thy [wfrec_def,wftrec_def,the_recfun_def,is_recfun_def]
+    "[| r=r';  !!x u. H(x,u)=H'(x,u);  a=a' |] \
+\    ==> wfrec(r,a,H)=wfrec(r',a',H')";
+by (EVERY1 (map rtac (prems RL [subst])));
+by (SIMP_TAC (wf_ss addrews (prems RL [sym])) 1);
+val wfrec_cong = result();