(* Title: CCL/fix
ID: $Id$
Author: Martin Coen, Cambridge University Computer Laboratory
Copyright 1993 University of Cambridge
For fix.thy.
*)
open Fix;
(*** Fixed Point Induction ***)
val [base,step,incl] = goalw Fix.thy [INCL_def]
"[| P(bot); !!x. P(x) ==> P(f(x)); INCL(P) |] ==> P(fix(f))";
by (rtac (incl RS spec RS mp) 1);
by (rtac (Nat_ind RS ballI) 1 THEN atac 1);
by (ALLGOALS (simp_tac term_ss));
by (REPEAT (ares_tac [base,step] 1));
qed "fix_ind";
(*** Inclusive Predicates ***)
val prems = goalw Fix.thy [INCL_def]
"INCL(P) <-> (ALL f. (ALL n:Nat. P(f ^ n ` bot)) --> P(fix(f)))";
by (rtac iff_refl 1);
qed "inclXH";
val prems = goal Fix.thy
"[| !!f. ALL n:Nat. P(f^n`bot) ==> P(fix(f)) |] ==> INCL(%x. P(x))";
by (fast_tac (term_cs addIs (prems @ [XH_to_I inclXH])) 1);
qed "inclI";
val incl::prems = goal Fix.thy
"[| INCL(P); !!n. n:Nat ==> P(f^n`bot) |] ==> P(fix(f))";
by (fast_tac (term_cs addIs ([ballI RS (incl RS (XH_to_D inclXH) RS spec RS mp)]
@ prems)) 1);
qed "inclD";
val incl::prems = goal Fix.thy
"[| INCL(P); (ALL n:Nat. P(f^n`bot))-->P(fix(f)) ==> R |] ==> R";
by (fast_tac (term_cs addIs ([incl RS inclD] @ prems)) 1);
qed "inclE";
(*** Lemmas for Inclusive Predicates ***)
goal Fix.thy "INCL(%x.~ a(x) [= t)";
by (rtac inclI 1);
by (dtac bspec 1);
by (rtac zeroT 1);
by (etac contrapos 1);
by (rtac po_trans 1);
by (assume_tac 2);
by (stac napplyBzero 1);
by (rtac po_cong 1 THEN rtac po_bot 1);
qed "npo_INCL";
val prems = goal Fix.thy "[| INCL(P); INCL(Q) |] ==> INCL(%x. P(x) & Q(x))";
by (fast_tac (set_cs addSIs ([inclI] @ (prems RL [inclD]))) 1);;
qed "conj_INCL";
val prems = goal Fix.thy "[| !!a. INCL(P(a)) |] ==> INCL(%x. ALL a. P(a,x))";
by (fast_tac (set_cs addSIs ([inclI] @ (prems RL [inclD]))) 1);;
qed "all_INCL";
val prems = goal Fix.thy "[| !!a. a:A ==> INCL(P(a)) |] ==> INCL(%x. ALL a:A. P(a,x))";
by (fast_tac (set_cs addSIs ([inclI] @ (prems RL [inclD]))) 1);;
qed "ball_INCL";
goal Fix.thy "INCL(%x. a(x) = (b(x)::'a::prog))";
by (simp_tac (term_ss addsimps [eq_iff]) 1);
by (REPEAT (resolve_tac [conj_INCL,po_INCL] 1));
qed "eq_INCL";
(*** Derivation of Reachability Condition ***)
(* Fixed points of idgen *)
goal Fix.thy "idgen(fix(idgen)) = fix(idgen)";
by (rtac (fixB RS sym) 1);
qed "fix_idgenfp";
goalw Fix.thy [idgen_def] "idgen(lam x. x) = lam x. x";
by (simp_tac term_ss 1);
by (rtac (term_case RS allI) 1);
by (ALLGOALS (simp_tac term_ss));
qed "id_idgenfp";
(* All fixed points are lam-expressions *)
val [prem] = goal Fix.thy "idgen(d) = d ==> d = lam x.?f(x)";
by (rtac (prem RS subst) 1);
by (rewtac idgen_def);
by (rtac refl 1);
qed "idgenfp_lam";
(* Lemmas for rewriting fixed points of idgen *)
val prems = goalw Fix.thy [idgen_def]
"[| a = b; a ` t = u |] ==> b ` t = u";
by (simp_tac (term_ss addsimps (prems RL [sym])) 1);
qed "l_lemma";
val idgen_lemmas =
let fun mk_thm s = prove_goalw Fix.thy [idgen_def] s
(fn [prem] => [rtac (prem RS l_lemma) 1,simp_tac term_ss 1])
in map mk_thm
[ "idgen(d) = d ==> d ` bot = bot",
"idgen(d) = d ==> d ` true = true",
"idgen(d) = d ==> d ` false = false",
"idgen(d) = d ==> d ` <a,b> = <d ` a,d ` b>",
"idgen(d) = d ==> d ` (lam x. f(x)) = lam x. d ` f(x)"]
end;
(* Proof of Reachability law - show that fix and lam x.x both give LEAST fixed points
of idgen and hence are they same *)
val [p1,p2,p3] = goal CCL.thy
"[| ALL x. t ` x [= u ` x; EX f. t=lam x. f(x); EX f. u=lam x. f(x) |] ==> t [= u";
by (stac (p2 RS cond_eta) 1);
by (stac (p3 RS cond_eta) 1);
by (rtac (p1 RS (po_lam RS iffD2)) 1);
qed "po_eta";
val [prem] = goalw Fix.thy [idgen_def] "idgen(d) = d ==> d = lam x.?f(x)";
by (rtac (prem RS subst) 1);
by (rtac refl 1);
qed "po_eta_lemma";
val [prem] = goal Fix.thy
"idgen(d) = d ==> \
\ {p. EX a b. p=<a,b> & (EX t. a=fix(idgen) ` t & b = d ` t)} <= \
\ POgen({p. EX a b. p=<a,b> & (EX t. a=fix(idgen) ` t & b = d ` t)})";
by (REPEAT (step_tac term_cs 1));
by (term_case_tac "t" 1);
by (ALLGOALS (simp_tac (term_ss addsimps (POgenXH::([prem,fix_idgenfp] RL idgen_lemmas)))));
by (ALLGOALS (fast_tac set_cs));
qed "lemma1";
val [prem] = goal Fix.thy
"idgen(d) = d ==> fix(idgen) [= d";
by (rtac (allI RS po_eta) 1);
by (rtac (lemma1 RSN(2,po_coinduct)) 1);
by (ALLGOALS (fast_tac (term_cs addIs [prem,po_eta_lemma,fix_idgenfp])));
qed "fix_least_idgen";
val [prem] = goal Fix.thy
"idgen(d) = d ==> \
\ {p. EX a b. p=<a,b> & b = d ` a} <= POgen({p. EX a b. p=<a,b> & b = d ` a})";
by (REPEAT (step_tac term_cs 1));
by (term_case_tac "a" 1);
by (ALLGOALS (simp_tac (term_ss addsimps (POgenXH::([prem] RL idgen_lemmas)))));
by (ALLGOALS (fast_tac set_cs));
qed "lemma2";
val [prem] = goal Fix.thy
"idgen(d) = d ==> lam x. x [= d";
by (rtac (allI RS po_eta) 1);
by (rtac (lemma2 RSN(2,po_coinduct)) 1);
by (simp_tac term_ss 1);
by (ALLGOALS (fast_tac (term_cs addIs [prem,po_eta_lemma,fix_idgenfp])));
qed "id_least_idgen";
goal Fix.thy "fix(idgen) = lam x. x";
by (fast_tac (term_cs addIs [eq_iff RS iffD2,
id_idgenfp RS fix_least_idgen,
fix_idgenfp RS id_least_idgen]) 1);
qed "reachability";
(********)
val [prem] = goal Fix.thy "f = lam x. x ==> f`t = t";
by (rtac (prem RS sym RS subst) 1);
by (rtac applyB 1);
qed "id_apply";
val prems = goal Fix.thy
"[| P(bot); P(true); P(false); \
\ !!x y.[| P(x); P(y) |] ==> P(<x,y>); \
\ !!u.(!!x. P(u(x))) ==> P(lam x. u(x)); INCL(P) |] ==> \
\ P(t)";
by (rtac (reachability RS id_apply RS subst) 1);
by (res_inst_tac [("x","t")] spec 1);
by (rtac fix_ind 1);
by (rewtac idgen_def);
by (REPEAT_SOME (ares_tac [allI]));
by (stac applyBbot 1);
by (resolve_tac prems 1);
br (applyB RS ssubst )1;
by (res_inst_tac [("t","xa")] term_case 1);
by (ALLGOALS (simp_tac term_ss));
by (ALLGOALS (fast_tac (term_cs addIs ([all_INCL,INCL_subst] @ prems))));
qed "term_ind";