1 (* Title: HOL/Tools/meson.ML
3 Author: Lawrence C Paulson, Cambridge University Computer Laboratory
4 Copyright 1992 University of Cambridge
6 The MESON resolution proof procedure for HOL.
8 When making clauses, avoids using the rewriter -- instead uses RS recursively
10 NEED TO SORT LITERALS BY # OF VARS, USING ==>I/E. ELIMINATES NEED FOR
11 FUNCTION nodups -- if done to goal clauses too!
16 val term_pair_of: indexname * (typ * 'a) -> term * 'a
17 val first_order_resolve: thm -> thm -> thm
18 val flexflex_first_order: thm -> thm
19 val size_of_subgoals: thm -> int
20 val make_cnf: thm list -> thm -> thm list
21 val finish_cnf: thm list -> thm list
22 val generalize: thm -> thm
23 val make_nnf: thm -> thm
24 val make_nnf1: thm -> thm
25 val skolemize: thm -> thm
26 val is_fol_term: theory -> term -> bool
27 val make_clauses: thm list -> thm list
28 val make_horns: thm list -> thm list
29 val best_prolog_tac: (thm -> int) -> thm list -> tactic
30 val depth_prolog_tac: thm list -> tactic
31 val gocls: thm list -> thm list
32 val skolemize_prems_tac: thm list -> int -> tactic
33 val MESON: (thm list -> thm list) -> (thm list -> tactic) -> int -> tactic
34 val best_meson_tac: (thm -> int) -> int -> tactic
35 val safe_best_meson_tac: int -> tactic
36 val depth_meson_tac: int -> tactic
37 val prolog_step_tac': thm list -> int -> tactic
38 val iter_deepen_prolog_tac: thm list -> tactic
39 val iter_deepen_meson_tac: thm list -> int -> tactic
40 val make_meta_clause: thm -> thm
41 val make_meta_clauses: thm list -> thm list
42 val meson_claset_tac: thm list -> claset -> int -> tactic
43 val meson_tac: int -> tactic
44 val negate_head: thm -> thm
45 val select_literal: int -> thm -> thm
46 val skolemize_tac: int -> tactic
49 structure Meson: MESON =
52 val not_conjD = thm "meson_not_conjD";
53 val not_disjD = thm "meson_not_disjD";
54 val not_notD = thm "meson_not_notD";
55 val not_allD = thm "meson_not_allD";
56 val not_exD = thm "meson_not_exD";
57 val imp_to_disjD = thm "meson_imp_to_disjD";
58 val not_impD = thm "meson_not_impD";
59 val iff_to_disjD = thm "meson_iff_to_disjD";
60 val not_iffD = thm "meson_not_iffD";
61 val conj_exD1 = thm "meson_conj_exD1";
62 val conj_exD2 = thm "meson_conj_exD2";
63 val disj_exD = thm "meson_disj_exD";
64 val disj_exD1 = thm "meson_disj_exD1";
65 val disj_exD2 = thm "meson_disj_exD2";
66 val disj_assoc = thm "meson_disj_assoc";
67 val disj_comm = thm "meson_disj_comm";
68 val disj_FalseD1 = thm "meson_disj_FalseD1";
69 val disj_FalseD2 = thm "meson_disj_FalseD2";
72 (**** Operators for forward proof ****)
75 (** First-order Resolution **)
77 fun typ_pair_of (ix, (sort,ty)) = (TVar (ix,sort), ty);
78 fun term_pair_of (ix, (ty,t)) = (Var (ix,ty), t);
80 val Envir.Envir {asol = tenv0, iTs = tyenv0, ...} = Envir.empty 0
82 (*FIXME: currently does not "rename variables apart"*)
83 fun first_order_resolve thA thB =
84 let val thy = theory_of_thm thA
85 val tmA = concl_of thA
86 val Const("==>",_) $ tmB $ _ = prop_of thB
87 val (tyenv,tenv) = Pattern.first_order_match thy (tmB,tmA) (tyenv0,tenv0)
88 val ct_pairs = map (pairself (cterm_of thy) o term_pair_of) (Vartab.dest tenv)
89 in thA RS (cterm_instantiate ct_pairs thB) end
90 handle _ => raise THM ("first_order_resolve", 0, [thA,thB]);
92 fun flexflex_first_order th =
93 case (tpairs_of th) of
96 let val thy = theory_of_thm th
98 foldl (uncurry (Pattern.first_order_match thy)) (tyenv0,tenv0) pairs
99 val t_pairs = map term_pair_of (Vartab.dest tenv)
100 val th' = Thm.instantiate ([], map (pairself (cterm_of thy)) t_pairs) th
104 (*raises exception if no rules apply -- unlike RL*)
105 fun tryres (th, rls) =
106 let fun tryall [] = raise THM("tryres", 0, th::rls)
107 | tryall (rl::rls) = (th RS rl handle THM _ => tryall rls)
110 (*Permits forward proof from rules that discharge assumptions. The supplied proof state st,
111 e.g. from conj_forward, should have the form
112 "[| P' ==> ?P; Q' ==> ?Q |] ==> ?P & ?Q"
113 and the effect should be to instantiate ?P and ?Q with normalized versions of P' and Q'.*)
114 fun forward_res nf st =
115 let fun forward_tacf [prem] = rtac (nf prem) 1
116 | forward_tacf prems =
117 error ("Bad proof state in forward_res, please inform lcp@cl.cam.ac.uk:\n" ^
120 cat_lines (map string_of_thm prems))
122 case Seq.pull (ALLGOALS (METAHYPS forward_tacf) st)
124 | NONE => raise THM("forward_res", 0, [st])
127 (*Are any of the logical connectives in "bs" present in the term?*)
129 let fun has (Const(a,_)) = false
130 | has (Const("Trueprop",_) $ p) = has p
131 | has (Const("Not",_) $ p) = has p
132 | has (Const("op |",_) $ p $ q) = member (op =) bs "op |" orelse has p orelse has q
133 | has (Const("op &",_) $ p $ q) = member (op =) bs "op &" orelse has p orelse has q
134 | has (Const("All",_) $ Abs(_,_,p)) = member (op =) bs "All" orelse has p
135 | has (Const("Ex",_) $ Abs(_,_,p)) = member (op =) bs "Ex" orelse has p
140 (**** Clause handling ****)
142 fun literals (Const("Trueprop",_) $ P) = literals P
143 | literals (Const("op |",_) $ P $ Q) = literals P @ literals Q
144 | literals (Const("Not",_) $ P) = [(false,P)]
145 | literals P = [(true,P)];
147 (*number of literals in a term*)
148 val nliterals = length o literals;
151 (*** Tautology Checking ***)
153 fun signed_lits_aux (Const ("op |", _) $ P $ Q) (poslits, neglits) =
154 signed_lits_aux Q (signed_lits_aux P (poslits, neglits))
155 | signed_lits_aux (Const("Not",_) $ P) (poslits, neglits) = (poslits, P::neglits)
156 | signed_lits_aux P (poslits, neglits) = (P::poslits, neglits);
158 fun signed_lits th = signed_lits_aux (HOLogic.dest_Trueprop (concl_of th)) ([],[]);
160 (*Literals like X=X are tautologous*)
161 fun taut_poslit (Const("op =",_) $ t $ u) = t aconv u
162 | taut_poslit (Const("True",_)) = true
163 | taut_poslit _ = false;
166 let val (poslits,neglits) = signed_lits th
167 in exists taut_poslit poslits
169 exists (member (op aconv) neglits) (HOLogic.false_const :: poslits)
171 handle TERM _ => false; (*probably dest_Trueprop on a weird theorem*)
174 (*** To remove trivial negated equality literals from clauses ***)
176 (*They are typically functional reflexivity axioms and are the converses of
177 injectivity equivalences*)
179 val not_refl_disj_D = thm"meson_not_refl_disj_D";
181 (*Is either term a Var that does not properly occur in the other term?*)
182 fun eliminable (t as Var _, u) = t aconv u orelse not (Logic.occs(t,u))
183 | eliminable (u, t as Var _) = t aconv u orelse not (Logic.occs(t,u))
184 | eliminable _ = false;
186 fun refl_clause_aux 0 th = th
187 | refl_clause_aux n th =
188 case HOLogic.dest_Trueprop (concl_of th) of
189 (Const ("op |", _) $ (Const ("op |", _) $ _ $ _) $ _) =>
190 refl_clause_aux n (th RS disj_assoc) (*isolate an atom as first disjunct*)
191 | (Const ("op |", _) $ (Const("Not",_) $ (Const("op =",_) $ t $ u)) $ _) =>
193 then refl_clause_aux (n-1) (th RS not_refl_disj_D) (*Var inequation: delete*)
194 else refl_clause_aux (n-1) (th RS disj_comm) (*not between Vars: ignore*)
195 | (Const ("op |", _) $ _ $ _) => refl_clause_aux n (th RS disj_comm)
196 | _ => (*not a disjunction*) th;
198 fun notequal_lits_count (Const ("op |", _) $ P $ Q) =
199 notequal_lits_count P + notequal_lits_count Q
200 | notequal_lits_count (Const("Not",_) $ (Const("op =",_) $ _ $ _)) = 1
201 | notequal_lits_count _ = 0;
203 (*Simplify a clause by applying reflexivity to its negated equality literals*)
205 let val neqs = notequal_lits_count (HOLogic.dest_Trueprop (concl_of th))
206 in zero_var_indexes (refl_clause_aux neqs th) end
207 handle TERM _ => th; (*probably dest_Trueprop on a weird theorem*)
210 (*** The basic CNF transformation ***)
212 val max_clauses = 40;
214 fun sum x y = if x < max_clauses andalso y < max_clauses then x+y else max_clauses;
215 fun prod x y = if x < max_clauses andalso y < max_clauses then x*y else max_clauses;
217 (*Estimate the number of clauses in order to detect infeasible theorems*)
218 fun signed_nclauses b (Const("Trueprop",_) $ t) = signed_nclauses b t
219 | signed_nclauses b (Const("Not",_) $ t) = signed_nclauses (not b) t
220 | signed_nclauses b (Const("op &",_) $ t $ u) =
221 if b then sum (signed_nclauses b t) (signed_nclauses b u)
222 else prod (signed_nclauses b t) (signed_nclauses b u)
223 | signed_nclauses b (Const("op |",_) $ t $ u) =
224 if b then prod (signed_nclauses b t) (signed_nclauses b u)
225 else sum (signed_nclauses b t) (signed_nclauses b u)
226 | signed_nclauses b (Const("op -->",_) $ t $ u) =
227 if b then prod (signed_nclauses (not b) t) (signed_nclauses b u)
228 else sum (signed_nclauses (not b) t) (signed_nclauses b u)
229 | signed_nclauses b (Const("op =", Type ("fun", [T, _])) $ t $ u) =
230 if T = HOLogic.boolT then (*Boolean equality is if-and-only-if*)
231 if b then sum (prod (signed_nclauses (not b) t) (signed_nclauses b u))
232 (prod (signed_nclauses (not b) u) (signed_nclauses b t))
233 else sum (prod (signed_nclauses b t) (signed_nclauses b u))
234 (prod (signed_nclauses (not b) t) (signed_nclauses (not b) u))
236 | signed_nclauses b (Const("Ex", _) $ Abs (_,_,t)) = signed_nclauses b t
237 | signed_nclauses b (Const("All",_) $ Abs (_,_,t)) = signed_nclauses b t
238 | signed_nclauses _ _ = 1; (* literal *)
240 val nclauses = signed_nclauses true;
242 fun too_many_clauses t = nclauses t >= max_clauses;
244 (*Replaces universally quantified variables by FREE variables -- because
245 assumptions may not contain scheme variables. Later, we call "generalize". *)
247 let val newname = gensym "mes_"
248 val spec' = read_instantiate [("x", newname)] spec
251 (*Used with METAHYPS below. There is one assumption, which gets bound to prem
252 and then normalized via function nf. The normal form is given to resolve_tac,
253 instantiate a Boolean variable created by resolution with disj_forward. Since
254 (nf prem) returns a LIST of theorems, we can backtrack to get all combinations.*)
255 fun resop nf [prem] = resolve_tac (nf prem) 1;
257 (*Any need to extend this list with
258 "HOL.type_class","HOL.eq_class","ProtoPure.term"?*)
260 exists_Const (member (op =) ["==", "==>", "all", "prop"] o #1);
262 fun apply_skolem_ths (th, rls) =
263 let fun tryall [] = raise THM("apply_skolem_ths", 0, th::rls)
264 | tryall (rl::rls) = (first_order_resolve th rl handle THM _ => tryall rls)
267 (*Conjunctive normal form, adding clauses from th in front of ths (for foldr).
268 Strips universal quantifiers and breaks up conjunctions.
269 Eliminates existential quantifiers using skoths: Skolemization theorems.*)
270 fun cnf skoths (th,ths) =
271 let fun cnf_aux (th,ths) =
272 if not (can HOLogic.dest_Trueprop (prop_of th)) then ths (*meta-level: ignore*)
273 else if not (has_conns ["All","Ex","op &"] (prop_of th))
274 then th::ths (*no work to do, terminate*)
275 else case head_of (HOLogic.dest_Trueprop (concl_of th)) of
276 Const ("op &", _) => (*conjunction*)
277 cnf_aux (th RS conjunct1, cnf_aux (th RS conjunct2, ths))
278 | Const ("All", _) => (*universal quantifier*)
279 cnf_aux (freeze_spec th, ths)
281 (*existential quantifier: Insert Skolem functions*)
282 cnf_aux (apply_skolem_ths (th,skoths), ths)
283 | Const ("op |", _) =>
284 (*Disjunction of P, Q: Create new goal of proving ?P | ?Q and solve it using
285 all combinations of converting P, Q to CNF.*)
287 (METAHYPS (resop cnf_nil) 1) THEN
288 (fn st' => st' |> METAHYPS (resop cnf_nil) 1)
289 in Seq.list_of (tac (th RS disj_forward)) @ ths end
290 | _ => (*no work to do*) th::ths
291 and cnf_nil th = cnf_aux (th,[])
293 if too_many_clauses (concl_of th)
294 then (Output.debug (fn () => ("cnf is ignoring: " ^ string_of_thm th)); ths)
295 else cnf_aux (th,ths)
298 fun all_names (Const ("all", _) $ Abs(x,_,P)) = x :: all_names P
301 fun new_names n [] = []
302 | new_names n (x::xs) =
303 if String.isPrefix "mes_" x then (x, radixstring(26,"A",n)) :: new_names (n+1) xs
306 (*The gensym names are ugly, so don't let the user see them. When forall_elim_vars
307 is called, it will ensure that no name clauses ensue.*)
309 let val old_names = all_names (prop_of th)
310 in Drule.rename_bvars (new_names 0 old_names) th end;
312 (*Convert all suitable free variables to schematic variables,
313 but don't discharge assumptions.*)
314 fun generalize th = Thm.varifyT (forall_elim_vars 0 (nice_names (forall_intr_frees th)));
316 fun make_cnf skoths th = cnf skoths (th, []);
318 (*Generalization, removal of redundant equalities, removal of tautologies.*)
319 fun finish_cnf ths = filter (not o is_taut) (map (refl_clause o generalize) ths);
322 (**** Removal of duplicate literals ****)
324 (*Forward proof, passing extra assumptions as theorems to the tactic*)
325 fun forward_res2 nf hyps st =
328 (METAHYPS (fn major::minors => rtac (nf (minors@hyps) major) 1) 1)
331 | NONE => raise THM("forward_res2", 0, [st]);
333 (*Remove duplicates in P|Q by assuming ~P in Q
334 rls (initially []) accumulates assumptions of the form P==>False*)
335 fun nodups_aux rls th = nodups_aux rls (th RS disj_assoc)
336 handle THM _ => tryres(th,rls)
337 handle THM _ => tryres(forward_res2 nodups_aux rls (th RS disj_forward2),
338 [disj_FalseD1, disj_FalseD2, asm_rl])
341 (*Remove duplicate literals, if there are any*)
343 if has_duplicates (op =) (literals (prop_of th))
344 then nodups_aux [] th
348 (**** Generation of contrapositives ****)
350 fun is_left (Const ("Trueprop", _) $
351 (Const ("op |", _) $ (Const ("op |", _) $ _ $ _) $ _)) = true
354 (*Associate disjuctions to right -- make leftmost disjunct a LITERAL*)
356 if is_left (prop_of th) then assoc_right (th RS disj_assoc)
359 (*Must check for negative literal first!*)
360 val clause_rules = [disj_assoc, make_neg_rule, make_pos_rule];
362 (*For ordinary resolution. *)
363 val resolution_clause_rules = [disj_assoc, make_neg_rule', make_pos_rule'];
365 (*Create a goal or support clause, conclusing False*)
366 fun make_goal th = (*Must check for negative literal first!*)
367 make_goal (tryres(th, clause_rules))
368 handle THM _ => tryres(th, [make_neg_goal, make_pos_goal]);
370 (*Sort clauses by number of literals*)
371 fun fewerlits(th1,th2) = nliterals(prop_of th1) < nliterals(prop_of th2);
373 fun sort_clauses ths = sort (make_ord fewerlits) ths;
375 (*True if the given type contains bool anywhere*)
376 fun has_bool (Type("bool",_)) = true
377 | has_bool (Type(_, Ts)) = exists has_bool Ts
378 | has_bool _ = false;
380 (*Is the string the name of a connective? Really only | and Not can remain,
381 since this code expects to be called on a clause form.*)
382 val is_conn = member (op =)
383 ["Trueprop", "op &", "op |", "op -->", "Not",
384 "All", "Ex", "Ball", "Bex"];
386 (*True if the term contains a function--not a logical connective--where the type
387 of any argument contains bool.*)
388 val has_bool_arg_const =
390 (fn (c,T) => not(is_conn c) andalso exists (has_bool) (binder_types T));
392 (*A higher-order instance of a first-order constant? Example is the definition of
393 HOL.one, 1, at a function type in theory SetsAndFunctions.*)
394 fun higher_inst_const thy (c,T) =
395 case binder_types T of
396 [] => false (*not a function type, OK*)
397 | Ts => length (binder_types (Sign.the_const_type thy c)) <> length Ts;
399 (*Returns false if any Vars in the theorem mention type bool.
400 Also rejects functions whose arguments are Booleans or other functions.*)
401 fun is_fol_term thy t =
402 Term.is_first_order ["all","All","Ex"] t andalso
403 not (exists (has_bool o fastype_of) (term_vars t) orelse
404 has_bool_arg_const t orelse
405 exists_Const (higher_inst_const thy) t orelse
408 fun rigid t = not (is_Var (head_of t));
410 fun ok4horn (Const ("Trueprop",_) $ (Const ("op |", _) $ t $ _)) = rigid t
411 | ok4horn (Const ("Trueprop",_) $ t) = rigid t
414 (*Create a meta-level Horn clause*)
415 fun make_horn crules th =
416 if ok4horn (concl_of th)
417 then make_horn crules (tryres(th,crules)) handle THM _ => th
420 (*Generate Horn clauses for all contrapositives of a clause. The input, th,
421 is a HOL disjunction.*)
422 fun add_contras crules (th,hcs) =
423 let fun rots (0,th) = hcs
424 | rots (k,th) = zero_var_indexes (make_horn crules th) ::
425 rots(k-1, assoc_right (th RS disj_comm))
426 in case nliterals(prop_of th) of
428 | n => rots(n, assoc_right th)
431 (*Use "theorem naming" to label the clauses*)
432 fun name_thms label =
433 let fun name1 (th, (k,ths)) =
434 (k-1, PureThy.put_name_hint (label ^ string_of_int k) th :: ths)
435 in fn ths => #2 (foldr name1 (length ths, []) ths) end;
437 (*Is the given disjunction an all-negative support clause?*)
438 fun is_negative th = forall (not o #1) (literals (prop_of th));
440 val neg_clauses = List.filter is_negative;
443 (***** MESON PROOF PROCEDURE *****)
445 fun rhyps (Const("==>",_) $ (Const("Trueprop",_) $ A) $ phi,
446 As) = rhyps(phi, A::As)
447 | rhyps (_, As) = As;
449 (** Detecting repeated assumptions in a subgoal **)
451 (*The stringtree detects repeated assumptions.*)
452 fun ins_term (net,t) = Net.insert_term (op aconv) (t,t) net;
454 (*detects repetitions in a list of terms*)
455 fun has_reps [] = false
456 | has_reps [_] = false
457 | has_reps [t,u] = (t aconv u)
458 | has_reps ts = (Library.foldl ins_term (Net.empty, ts); false)
459 handle Net.INSERT => true;
461 (*Like TRYALL eq_assume_tac, but avoids expensive THEN calls*)
462 fun TRYING_eq_assume_tac 0 st = Seq.single st
463 | TRYING_eq_assume_tac i st =
464 TRYING_eq_assume_tac (i-1) (eq_assumption i st)
465 handle THM _ => TRYING_eq_assume_tac (i-1) st;
467 fun TRYALL_eq_assume_tac st = TRYING_eq_assume_tac (nprems_of st) st;
469 (*Loop checking: FAIL if trying to prove the same thing twice
470 -- if *ANY* subgoal has repeated literals*)
472 if exists (fn prem => has_reps (rhyps(prem,[]))) (prems_of st)
473 then Seq.empty else Seq.single st;
476 (* net_resolve_tac actually made it slower... *)
477 fun prolog_step_tac horns i =
478 (assume_tac i APPEND resolve_tac horns i) THEN check_tac THEN
479 TRYALL_eq_assume_tac;
481 (*Sums the sizes of the subgoals, ignoring hypotheses (ancestors)*)
482 fun addconcl(prem,sz) = size_of_term(Logic.strip_assums_concl prem) + sz
484 fun size_of_subgoals st = foldr addconcl 0 (prems_of st);
487 (*Negation Normal Form*)
488 val nnf_rls = [imp_to_disjD, iff_to_disjD, not_conjD, not_disjD,
489 not_impD, not_iffD, not_allD, not_exD, not_notD];
491 fun ok4nnf (Const ("Trueprop",_) $ (Const ("Not", _) $ t)) = rigid t
492 | ok4nnf (Const ("Trueprop",_) $ t) = rigid t
496 if ok4nnf (concl_of th)
497 then make_nnf1 (tryres(th, nnf_rls))
499 forward_res make_nnf1
500 (tryres(th, [conj_forward,disj_forward,all_forward,ex_forward]))
504 (*The simplification removes defined quantifiers and occurrences of True and False.
505 nnf_ss also includes the one-point simprocs,
506 which are needed to avoid the various one-point theorems from generating junk clauses.*)
508 [simp_implies_def, Ex1_def, Ball_def, Bex_def, if_True,
509 if_False, if_cancel, if_eq_cancel, cases_simp];
510 val nnf_extra_simps =
511 thms"split_ifs" @ ex_simps @ all_simps @ simp_thms;
514 HOL_basic_ss addsimps nnf_extra_simps
515 addsimprocs [defALL_regroup,defEX_regroup, @{simproc neq}, @{simproc let_simp}];
517 fun make_nnf th = case prems_of th of
518 [] => th |> rewrite_rule (map safe_mk_meta_eq nnf_simps)
521 | _ => raise THM ("make_nnf: premises in argument", 0, [th]);
523 (*Pull existential quantifiers to front. This accomplishes Skolemization for
524 clauses that arise from a subgoal.*)
526 if not (has_conns ["Ex"] (prop_of th)) then th
527 else (skolemize (tryres(th, [choice, conj_exD1, conj_exD2,
528 disj_exD, disj_exD1, disj_exD2])))
530 skolemize (forward_res skolemize
531 (tryres (th, [conj_forward, disj_forward, all_forward])))
532 handle THM _ => forward_res skolemize (th RS ex_forward);
535 (*Make clauses from a list of theorems, previously Skolemized and put into nnf.
536 The resulting clauses are HOL disjunctions.*)
537 fun make_clauses ths =
538 (sort_clauses (map (generalize o nodups) (foldr (cnf[]) [] ths)));
540 (*Convert a list of clauses (disjunctions) to Horn clauses (contrapositives)*)
543 (distinct Thm.eq_thm_prop (foldr (add_contras clause_rules) [] ths));
545 (*Could simply use nprems_of, which would count remaining subgoals -- no
546 discrimination as to their size! With BEST_FIRST, fails for problem 41.*)
548 fun best_prolog_tac sizef horns =
549 BEST_FIRST (has_fewer_prems 1, sizef) (prolog_step_tac horns 1);
551 fun depth_prolog_tac horns =
552 DEPTH_FIRST (has_fewer_prems 1) (prolog_step_tac horns 1);
554 (*Return all negative clauses, as possible goal clauses*)
555 fun gocls cls = name_thms "Goal#" (map make_goal (neg_clauses cls));
557 fun skolemize_prems_tac prems =
558 cut_facts_tac (map (skolemize o make_nnf) prems) THEN'
561 (*Basis of all meson-tactics. Supplies cltac with clauses: HOL disjunctions.
562 Function mkcl converts theorems to clauses.*)
563 fun MESON mkcl cltac i st =
565 (EVERY [ObjectLogic.atomize_prems_tac 1,
568 EVERY1 [skolemize_prems_tac negs,
569 METAHYPS (cltac o mkcl)]) 1]) i st
570 handle THM _ => no_tac st; (*probably from make_meta_clause, not first-order*)
572 (** Best-first search versions **)
574 (*ths is a list of additional clauses (HOL disjunctions) to use.*)
575 fun best_meson_tac sizef =
578 THEN_BEST_FIRST (resolve_tac (gocls cls) 1)
579 (has_fewer_prems 1, sizef)
580 (prolog_step_tac (make_horns cls) 1));
582 (*First, breaks the goal into independent units*)
583 val safe_best_meson_tac =
584 SELECT_GOAL (TRY (CLASET safe_tac) THEN
585 TRYALL (best_meson_tac size_of_subgoals));
587 (** Depth-first search version **)
589 val depth_meson_tac =
591 (fn cls => EVERY [resolve_tac (gocls cls) 1, depth_prolog_tac (make_horns cls)]);
594 (** Iterative deepening version **)
596 (*This version does only one inference per call;
597 having only one eq_assume_tac speeds it up!*)
598 fun prolog_step_tac' horns =
599 let val (horn0s, hornps) = (*0 subgoals vs 1 or more*)
600 take_prefix Thm.no_prems horns
601 val nrtac = net_resolve_tac horns
602 in fn i => eq_assume_tac i ORELSE
603 match_tac horn0s i ORELSE (*no backtracking if unit MATCHES*)
604 ((assume_tac i APPEND nrtac i) THEN check_tac)
607 fun iter_deepen_prolog_tac horns =
608 ITER_DEEPEN (has_fewer_prems 1) (prolog_step_tac' horns);
610 fun iter_deepen_meson_tac ths = MESON make_clauses
612 case (gocls (cls@ths)) of
613 [] => no_tac (*no goal clauses*)
615 let val horns = make_horns (cls@ths)
617 Output.debug (fn () => ("meson method called:\n" ^
618 space_implode "\n" (map string_of_thm (cls@ths)) ^
620 space_implode "\n" (map string_of_thm horns)))
621 in THEN_ITER_DEEPEN (resolve_tac goes 1) (has_fewer_prems 1) (prolog_step_tac' horns)
625 fun meson_claset_tac ths cs =
626 SELECT_GOAL (TRY (safe_tac cs) THEN TRYALL (iter_deepen_meson_tac ths));
628 val meson_tac = CLASET' (meson_claset_tac []);
631 (**** Code to support ordinary resolution, rather than Model Elimination ****)
633 (*Convert a list of clauses (disjunctions) to meta-level clauses (==>),
634 with no contrapositives, for ordinary resolution.*)
636 (*Rules to convert the head literal into a negated assumption. If the head
637 literal is already negated, then using notEfalse instead of notEfalse'
638 prevents a double negation.*)
639 val notEfalse = read_instantiate [("R","False")] notE;
640 val notEfalse' = rotate_prems 1 notEfalse;
642 fun negated_asm_of_head th =
643 th RS notEfalse handle THM _ => th RS notEfalse';
645 (*Converting one clause*)
646 val make_meta_clause =
647 zero_var_indexes o negated_asm_of_head o make_horn resolution_clause_rules;
649 fun make_meta_clauses ths =
651 (distinct Thm.eq_thm_prop (map make_meta_clause ths));
653 (*Permute a rule's premises to move the i-th premise to the last position.*)
655 let val n = nprems_of th
656 in if 1 <= i andalso i <= n
657 then Thm.permute_prems (i-1) 1 th
658 else raise THM("select_literal", i, [th])
661 (*Maps a rule that ends "... ==> P ==> False" to "... ==> ~P" while suppressing
663 val negate_head = rewrite_rule [atomize_not, not_not RS eq_reflection];
665 (*Maps the clause [P1,...Pn]==>False to [P1,...,P(i-1),P(i+1),...Pn] ==> ~P*)
666 fun select_literal i cl = negate_head (make_last i cl);
669 (*Top-level Skolemization. Allows part of the conversion to clauses to be
670 expressed as a tactic (or Isar method). Each assumption of the selected
671 goal is converted to NNF and then its existential quantifiers are pulled
672 to the front. Finally, all existential quantifiers are eliminated,
673 leaving !!-quantified variables. Perhaps Safe_tac should follow, but it
674 might generate many subgoals.*)
676 fun skolemize_tac i st =
677 let val ts = Logic.strip_assums_hyp (List.nth (prems_of st, i-1))
680 (fn hyps => (cut_facts_tac (map (skolemize o make_nnf) hyps) 1
681 THEN REPEAT (etac exE 1))),
682 REPEAT_DETERM_N (length ts) o (etac thin_rl)] i st
684 handle Subscript => Seq.empty;