src/HOL/Tools/meson.ML
author wenzelm
Tue Jun 13 23:41:37 2006 +0200 (2006-06-13)
changeset 19875 7405ce9d4f25
parent 19728 6c47d9295dca
child 19894 7c7e15b27145
permissions -rw-r--r--
avoid unqualified exception names;
tuned;
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(*  Title:      HOL/Tools/meson.ML
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    ID:         $Id$
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    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
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    Copyright   1992  University of Cambridge
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The MESON resolution proof procedure for HOL.
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When making clauses, avoids using the rewriter -- instead uses RS recursively
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NEED TO SORT LITERALS BY # OF VARS, USING ==>I/E.  ELIMINATES NEED FOR
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FUNCTION nodups -- if done to goal clauses too!
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*)
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signature BASIC_MESON =
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sig
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  val size_of_subgoals	: thm -> int
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  val make_cnf		: thm list -> thm -> thm list
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  val make_nnf		: thm -> thm
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  val make_nnf1		: thm -> thm
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  val skolemize		: thm -> thm
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  val make_clauses	: thm list -> thm list
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  val make_horns	: thm list -> thm list
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  val best_prolog_tac	: (thm -> int) -> thm list -> tactic
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  val depth_prolog_tac	: thm list -> tactic
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  val gocls		: thm list -> thm list
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  val skolemize_prems_tac	: thm list -> int -> tactic
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  val MESON		: (thm list -> tactic) -> int -> tactic
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  val best_meson_tac	: (thm -> int) -> int -> tactic
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  val safe_best_meson_tac	: int -> tactic
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  val depth_meson_tac	: int -> tactic
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  val prolog_step_tac'	: thm list -> int -> tactic
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  val iter_deepen_prolog_tac	: thm list -> tactic
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  val iter_deepen_meson_tac	: thm list -> int -> tactic
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  val meson_tac		: int -> tactic
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  val negate_head	: thm -> thm
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  val select_literal	: int -> thm -> thm
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  val skolemize_tac	: int -> tactic
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  val make_clauses_tac	: int -> tactic
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  val check_is_fol_term : term -> term
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end
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structure Meson =
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struct
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val not_conjD = thm "meson_not_conjD";
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val not_disjD = thm "meson_not_disjD";
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val not_notD = thm "meson_not_notD";
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val not_allD = thm "meson_not_allD";
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val not_exD = thm "meson_not_exD";
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val imp_to_disjD = thm "meson_imp_to_disjD";
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val not_impD = thm "meson_not_impD";
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val iff_to_disjD = thm "meson_iff_to_disjD";
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val not_iffD = thm "meson_not_iffD";
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val conj_exD1 = thm "meson_conj_exD1";
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val conj_exD2 = thm "meson_conj_exD2";
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val disj_exD = thm "meson_disj_exD";
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val disj_exD1 = thm "meson_disj_exD1";
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val disj_exD2 = thm "meson_disj_exD2";
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val disj_assoc = thm "meson_disj_assoc";
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val disj_comm = thm "meson_disj_comm";
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val disj_FalseD1 = thm "meson_disj_FalseD1";
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val disj_FalseD2 = thm "meson_disj_FalseD2";
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val depth_limit = ref 2000;
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(**** Operators for forward proof ****)
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(*Like RS, but raises Option if there are no unifiers and allows multiple unifiers.*)
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fun resolve1 (tha,thb) = Seq.hd (biresolution false [(false,tha)] 1 thb);
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(*raises exception if no rules apply -- unlike RL*)
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fun tryres (th, rls) = 
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  let fun tryall [] = raise THM("tryres", 0, th::rls)
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        | tryall (rl::rls) = (resolve1(th,rl) handle Option.Option => tryall rls)
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  in  tryall rls  end;
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(*Permits forward proof from rules that discharge assumptions*)
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fun forward_res nf st =
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  case Seq.pull (ALLGOALS (METAHYPS (fn [prem] => rtac (nf prem) 1)) st)
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  of SOME(th,_) => th
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   | NONE => raise THM("forward_res", 0, [st]);
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(*Are any of the constants in "bs" present in the term?*)
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fun has_consts bs =
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  let fun has (Const(a,_)) = member (op =) bs a
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	| has (Const ("Hilbert_Choice.Eps",_) $ _) = false
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		     (*ignore constants within @-terms*)
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	| has (f$u) = has f orelse has u
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	| has (Abs(_,_,t)) = has t
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	| has _ = false
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  in  has  end;
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(**** Clause handling ****)
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fun literals (Const("Trueprop",_) $ P) = literals P
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  | literals (Const("op |",_) $ P $ Q) = literals P @ literals Q
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  | literals (Const("Not",_) $ P) = [(false,P)]
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  | literals P = [(true,P)];
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(*number of literals in a term*)
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val nliterals = length o literals;
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(*** Tautology Checking ***)
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fun signed_lits_aux (Const ("op |", _) $ P $ Q) (poslits, neglits) = 
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      signed_lits_aux Q (signed_lits_aux P (poslits, neglits))
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  | signed_lits_aux (Const("Not",_) $ P) (poslits, neglits) = (poslits, P::neglits)
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  | signed_lits_aux P (poslits, neglits) = (P::poslits, neglits);
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fun signed_lits th = signed_lits_aux (HOLogic.dest_Trueprop (concl_of th)) ([],[]);
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(*Literals like X=X are tautologous*)
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fun taut_poslit (Const("op =",_) $ t $ u) = t aconv u
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  | taut_poslit (Const("True",_)) = true
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  | taut_poslit _ = false;
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fun is_taut th =
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  let val (poslits,neglits) = signed_lits th
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  in  exists taut_poslit poslits
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      orelse
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      exists (fn t => mem_term (t, neglits)) (HOLogic.false_const :: poslits)
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  end;
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(*** To remove trivial negated equality literals from clauses ***)
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(*They are typically functional reflexivity axioms and are the converses of
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  injectivity equivalences*)
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val not_refl_disj_D = thm"meson_not_refl_disj_D";
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fun refl_clause_aux 0 th = th
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  | refl_clause_aux n th =
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       case HOLogic.dest_Trueprop (concl_of th) of
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	  (Const ("op |", _) $ (Const ("op |", _) $ _ $ _) $ _) => 
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            refl_clause_aux n (th RS disj_assoc)    (*isolate an atom as first disjunct*)
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	| (Const ("op |", _) $ (Const("Not",_) $ (Const("op =",_) $ t $ u)) $ _) => 
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	    if is_Var t orelse is_Var u then (*Var inequation: delete or ignore*)
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		(refl_clause_aux (n-1) (th RS not_refl_disj_D)    (*delete*)
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		 handle THM _ => refl_clause_aux (n-1) (th RS disj_comm))  (*ignore*)
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	    else refl_clause_aux (n-1) (th RS disj_comm)  (*not between Vars: ignore*)
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	| (Const ("op |", _) $ _ $ _) => refl_clause_aux n (th RS disj_comm)
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	| _ => (*not a disjunction*) th;
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fun notequal_lits_count (Const ("op |", _) $ P $ Q) = 
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      notequal_lits_count P + notequal_lits_count Q
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  | notequal_lits_count (Const("Not",_) $ (Const("op =",_) $ _ $ _)) = 1
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  | notequal_lits_count _ = 0;
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(*Simplify a clause by applying reflexivity to its negated equality literals*)
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fun refl_clause th = 
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  let val neqs = notequal_lits_count (HOLogic.dest_Trueprop (concl_of th))
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  in  zero_var_indexes (refl_clause_aux neqs th)  end;
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(*** The basic CNF transformation ***)
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(*Replaces universally quantified variables by FREE variables -- because
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  assumptions may not contain scheme variables.  Later, call "generalize". *)
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fun freeze_spec th =
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  let val newname = gensym "A_"
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      val spec' = read_instantiate [("x", newname)] spec
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  in  th RS spec'  end;
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(*Used with METAHYPS below. There is one assumption, which gets bound to prem
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  and then normalized via function nf. The normal form is given to resolve_tac,
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  presumably to instantiate a Boolean variable.*)
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fun resop nf [prem] = resolve_tac (nf prem) 1;
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val has_meta_conn = 
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    exists_Const (fn (c,_) => c mem_string ["==", "==>", "all", "prop"]);
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(*Conjunctive normal form, adding clauses from th in front of ths (for foldr).
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  Strips universal quantifiers and breaks up conjunctions.
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  Eliminates existential quantifiers using skoths: Skolemization theorems.*)
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fun cnf skoths (th,ths) =
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  let fun cnf_aux (th,ths) =
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        if has_meta_conn (prop_of th) then ths (*meta-level: ignore*)
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        else if not (has_consts ["All","Ex","op &"] (prop_of th))  
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	then th::ths (*no work to do, terminate*)
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	else case head_of (HOLogic.dest_Trueprop (concl_of th)) of
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	    Const ("op &", _) => (*conjunction*)
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		cnf_aux (th RS conjunct1,
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			      cnf_aux (th RS conjunct2, ths))
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	  | Const ("All", _) => (*universal quantifier*)
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	        cnf_aux (freeze_spec th,  ths)
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	  | Const ("Ex", _) => 
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	      (*existential quantifier: Insert Skolem functions*)
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	      cnf_aux (tryres (th,skoths), ths)
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	  | Const ("op |", _) => (*disjunction*)
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	      let val tac =
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		  (METAHYPS (resop cnf_nil) 1) THEN
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		   (fn st' => st' |> METAHYPS (resop cnf_nil) 1)
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	      in  Seq.list_of (tac (th RS disj_forward)) @ ths  end 
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	  | _ => (*no work to do*) th::ths 
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      and cnf_nil th = cnf_aux (th,[])
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  in 
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    cnf_aux (th,ths)
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  end;
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(*Convert all suitable free variables to schematic variables, 
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  but don't discharge assumptions.*)
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fun generalize th = Thm.varifyT (forall_elim_vars 0 (forall_intr_frees th));
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fun make_cnf skoths th = 
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  filter (not o is_taut) 
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    (map (refl_clause o generalize) (cnf skoths (th, [])));
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(**** Removal of duplicate literals ****)
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(*Forward proof, passing extra assumptions as theorems to the tactic*)
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fun forward_res2 nf hyps st =
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  case Seq.pull
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	(REPEAT
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	 (METAHYPS (fn major::minors => rtac (nf (minors@hyps) major) 1) 1)
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	 st)
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  of SOME(th,_) => th
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   | NONE => raise THM("forward_res2", 0, [st]);
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(*Remove duplicates in P|Q by assuming ~P in Q
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  rls (initially []) accumulates assumptions of the form P==>False*)
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fun nodups_aux rls th = nodups_aux rls (th RS disj_assoc)
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    handle THM _ => tryres(th,rls)
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    handle THM _ => tryres(forward_res2 nodups_aux rls (th RS disj_forward2),
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			   [disj_FalseD1, disj_FalseD2, asm_rl])
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    handle THM _ => th;
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(*Remove duplicate literals, if there are any*)
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fun nodups th =
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    if null(findrep(literals(prop_of th))) then th
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    else nodups_aux [] th;
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(**** Generation of contrapositives ****)
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(*Associate disjuctions to right -- make leftmost disjunct a LITERAL*)
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fun assoc_right th = assoc_right (th RS disj_assoc)
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	handle THM _ => th;
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(*Must check for negative literal first!*)
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val clause_rules = [disj_assoc, make_neg_rule, make_pos_rule];
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(*For ordinary resolution. *)
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val resolution_clause_rules = [disj_assoc, make_neg_rule', make_pos_rule'];
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(*Create a goal or support clause, conclusing False*)
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fun make_goal th =   (*Must check for negative literal first!*)
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    make_goal (tryres(th, clause_rules))
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  handle THM _ => tryres(th, [make_neg_goal, make_pos_goal]);
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(*Sort clauses by number of literals*)
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fun fewerlits(th1,th2) = nliterals(prop_of th1) < nliterals(prop_of th2);
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fun sort_clauses ths = sort (make_ord fewerlits) ths;
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(*True if the given type contains bool anywhere*)
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fun has_bool (Type("bool",_)) = true
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  | has_bool (Type(_, Ts)) = exists has_bool Ts
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  | has_bool _ = false;
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(*Is the string the name of a connective? It doesn't matter if this list is
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  incomplete, since when actually called, the only connectives likely to
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  remain are & | Not.*)  
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val is_conn = member (op =)
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    ["Trueprop", "HOL.tag", "op &", "op |", "op -->", "op =", "Not", 
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     "All", "Ex", "Ball", "Bex"];
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(*True if the term contains a function where the type of any argument contains
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  bool.*)
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val has_bool_arg_const = 
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    exists_Const
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      (fn (c,T) => not(is_conn c) andalso exists (has_bool) (binder_types T));
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(*Raises an exception if any Vars in the theorem mention type bool; they
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  could cause make_horn to loop! Also rejects functions whose arguments are 
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  Booleans or other functions.*)
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fun is_fol_term t =
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    not (exists (has_bool o fastype_of) (term_vars t)  orelse
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	 not (Term.is_first_order ["all","All","Ex"] t) orelse
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	 has_bool_arg_const t  orelse  
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	 has_meta_conn t);
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(*FIXME: replace this by the boolean-valued version above!*)
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fun check_is_fol_term t =
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    if is_fol_term t then t else raise TERM("check_is_fol_term",[t]);
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fun check_is_fol th = (check_is_fol_term (prop_of th); th);
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(*Create a meta-level Horn clause*)
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fun make_horn crules th = make_horn crules (tryres(th,crules))
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			  handle THM _ => th;
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(*Generate Horn clauses for all contrapositives of a clause. The input, th,
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  is a HOL disjunction.*)
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fun add_contras crules (th,hcs) =
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  let fun rots (0,th) = hcs
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	| rots (k,th) = zero_var_indexes (make_horn crules th) ::
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			rots(k-1, assoc_right (th RS disj_comm))
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  in case nliterals(prop_of th) of
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	1 => th::hcs
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      | n => rots(n, assoc_right th)
paulson@15579
   308
  end;
paulson@9840
   309
paulson@15579
   310
(*Use "theorem naming" to label the clauses*)
paulson@15579
   311
fun name_thms label =
paulson@15579
   312
    let fun name1 (th, (k,ths)) =
paulson@15579
   313
	  (k-1, Thm.name_thm (label ^ string_of_int k, th) :: ths)
paulson@9840
   314
paulson@15579
   315
    in  fn ths => #2 (foldr name1 (length ths, []) ths)  end;
paulson@9840
   316
paulson@16563
   317
(*Is the given disjunction an all-negative support clause?*)
paulson@15579
   318
fun is_negative th = forall (not o #1) (literals (prop_of th));
paulson@9840
   319
paulson@15579
   320
val neg_clauses = List.filter is_negative;
paulson@9840
   321
paulson@9840
   322
paulson@15579
   323
(***** MESON PROOF PROCEDURE *****)
paulson@9840
   324
paulson@15579
   325
fun rhyps (Const("==>",_) $ (Const("Trueprop",_) $ A) $ phi,
paulson@15579
   326
	   As) = rhyps(phi, A::As)
paulson@15579
   327
  | rhyps (_, As) = As;
paulson@9840
   328
paulson@15579
   329
(** Detecting repeated assumptions in a subgoal **)
paulson@9840
   330
paulson@15579
   331
(*The stringtree detects repeated assumptions.*)
wenzelm@16801
   332
fun ins_term (net,t) = Net.insert_term (op aconv) (t,t) net;
paulson@9840
   333
paulson@15579
   334
(*detects repetitions in a list of terms*)
paulson@15579
   335
fun has_reps [] = false
paulson@15579
   336
  | has_reps [_] = false
paulson@15579
   337
  | has_reps [t,u] = (t aconv u)
paulson@15579
   338
  | has_reps ts = (Library.foldl ins_term (Net.empty, ts);  false)
wenzelm@19875
   339
		  handle Net.INSERT => true;
paulson@9840
   340
paulson@15579
   341
(*Like TRYALL eq_assume_tac, but avoids expensive THEN calls*)
paulson@18508
   342
fun TRYING_eq_assume_tac 0 st = Seq.single st
paulson@18508
   343
  | TRYING_eq_assume_tac i st =
paulson@18508
   344
       TRYING_eq_assume_tac (i-1) (eq_assumption i st)
paulson@18508
   345
       handle THM _ => TRYING_eq_assume_tac (i-1) st;
paulson@18508
   346
paulson@18508
   347
fun TRYALL_eq_assume_tac st = TRYING_eq_assume_tac (nprems_of st) st;
paulson@9840
   348
paulson@15579
   349
(*Loop checking: FAIL if trying to prove the same thing twice
paulson@15579
   350
  -- if *ANY* subgoal has repeated literals*)
paulson@15579
   351
fun check_tac st =
paulson@15579
   352
  if exists (fn prem => has_reps (rhyps(prem,[]))) (prems_of st)
paulson@15579
   353
  then  Seq.empty  else  Seq.single st;
paulson@9840
   354
paulson@9840
   355
paulson@15579
   356
(* net_resolve_tac actually made it slower... *)
paulson@15579
   357
fun prolog_step_tac horns i =
paulson@15579
   358
    (assume_tac i APPEND resolve_tac horns i) THEN check_tac THEN
paulson@18508
   359
    TRYALL_eq_assume_tac;
paulson@9840
   360
paulson@9840
   361
(*Sums the sizes of the subgoals, ignoring hypotheses (ancestors)*)
paulson@15579
   362
fun addconcl(prem,sz) = size_of_term(Logic.strip_assums_concl prem) + sz
paulson@15579
   363
paulson@15579
   364
fun size_of_subgoals st = foldr addconcl 0 (prems_of st);
paulson@15579
   365
paulson@9840
   366
paulson@9840
   367
(*Negation Normal Form*)
paulson@9840
   368
val nnf_rls = [imp_to_disjD, iff_to_disjD, not_conjD, not_disjD,
wenzelm@9869
   369
               not_impD, not_iffD, not_allD, not_exD, not_notD];
paulson@15581
   370
paulson@15581
   371
fun make_nnf1 th = make_nnf1 (tryres(th, nnf_rls))
wenzelm@9869
   372
    handle THM _ =>
paulson@15581
   373
        forward_res make_nnf1
wenzelm@9869
   374
           (tryres(th, [conj_forward,disj_forward,all_forward,ex_forward]))
paulson@9840
   375
    handle THM _ => th;
paulson@9840
   376
paulson@18405
   377
(*The simplification removes defined quantifiers and occurrences of True and False, 
paulson@18405
   378
  as well as tags applied to True and False. nnf_ss also includes the one-point simprocs,
paulson@18405
   379
  which are needed to avoid the various one-point theorems from generating junk clauses.*)
paulson@17404
   380
val tag_True = thm "tag_True";
paulson@17404
   381
val tag_False = thm "tag_False";
paulson@17404
   382
val nnf_simps = [Ex1_def,Ball_def,Bex_def,tag_True,tag_False]
paulson@18405
   383
paulson@18405
   384
val nnf_ss =
paulson@18405
   385
    HOL_basic_ss addsimps
paulson@18752
   386
     (nnf_simps @ [if_True, if_False, if_cancel, if_eq_cancel, cases_simp] @
paulson@18752
   387
      thms"split_ifs" @ ex_simps @ all_simps @ simp_thms)
paulson@18752
   388
     addsimprocs [defALL_regroup,defEX_regroup,neq_simproc,let_simproc];
paulson@15872
   389
paulson@15872
   390
fun make_nnf th = th |> simplify nnf_ss
mengj@18194
   391
                     |> make_nnf1
paulson@15581
   392
paulson@15965
   393
(*Pull existential quantifiers to front. This accomplishes Skolemization for
paulson@15965
   394
  clauses that arise from a subgoal.*)
wenzelm@9869
   395
fun skolemize th =
paulson@9840
   396
  if not (has_consts ["Ex"] (prop_of th)) then th
quigley@15773
   397
  else (skolemize (tryres(th, [choice, conj_exD1, conj_exD2,
quigley@15679
   398
                              disj_exD, disj_exD1, disj_exD2])))
wenzelm@9869
   399
    handle THM _ =>
wenzelm@9869
   400
        skolemize (forward_res skolemize
wenzelm@9869
   401
                   (tryres (th, [conj_forward, disj_forward, all_forward])))
paulson@9840
   402
    handle THM _ => forward_res skolemize (th RS ex_forward);
paulson@9840
   403
paulson@9840
   404
paulson@9840
   405
(*Make clauses from a list of theorems, previously Skolemized and put into nnf.
paulson@9840
   406
  The resulting clauses are HOL disjunctions.*)
wenzelm@9869
   407
fun make_clauses ths =
paulson@15998
   408
    (sort_clauses (map (generalize o nodups) (foldr (cnf[]) [] ths)));
quigley@15773
   409
paulson@9840
   410
paulson@16563
   411
(*Convert a list of clauses (disjunctions) to Horn clauses (contrapositives)*)
wenzelm@9869
   412
fun make_horns ths =
paulson@9840
   413
    name_thms "Horn#"
wenzelm@19046
   414
      (distinct Drule.eq_thm_prop (foldr (add_contras clause_rules) [] ths));
paulson@9840
   415
paulson@9840
   416
(*Could simply use nprems_of, which would count remaining subgoals -- no
paulson@9840
   417
  discrimination as to their size!  With BEST_FIRST, fails for problem 41.*)
paulson@9840
   418
wenzelm@9869
   419
fun best_prolog_tac sizef horns =
paulson@9840
   420
    BEST_FIRST (has_fewer_prems 1, sizef) (prolog_step_tac horns 1);
paulson@9840
   421
wenzelm@9869
   422
fun depth_prolog_tac horns =
paulson@9840
   423
    DEPTH_FIRST (has_fewer_prems 1) (prolog_step_tac horns 1);
paulson@9840
   424
paulson@9840
   425
(*Return all negative clauses, as possible goal clauses*)
paulson@9840
   426
fun gocls cls = name_thms "Goal#" (map make_goal (neg_clauses cls));
paulson@9840
   427
paulson@15008
   428
fun skolemize_prems_tac prems =
paulson@9840
   429
    cut_facts_tac (map (skolemize o make_nnf) prems)  THEN'
paulson@9840
   430
    REPEAT o (etac exE);
paulson@9840
   431
paulson@18141
   432
(*Expand all definitions (presumably of Skolem functions) in a proof state.*)
paulson@18141
   433
fun expand_defs_tac st =
paulson@18141
   434
  let val defs = filter (can dest_equals) (#hyps (crep_thm st))
wenzelm@18817
   435
  in  LocalDefs.def_export false defs st  end;
paulson@18141
   436
paulson@16588
   437
(*Basis of all meson-tactics.  Supplies cltac with clauses: HOL disjunctions*)
paulson@16588
   438
fun MESON cltac i st = 
paulson@16588
   439
  SELECT_GOAL
paulson@18141
   440
    (EVERY [rtac ccontr 1,
paulson@16588
   441
	    METAHYPS (fn negs =>
paulson@16588
   442
		      EVERY1 [skolemize_prems_tac negs,
paulson@18141
   443
			      METAHYPS (cltac o make_clauses)]) 1,
paulson@18141
   444
            expand_defs_tac]) i st
paulson@18508
   445
  handle TERM _ => no_tac st;	(*probably from check_is_fol*)		      
paulson@9840
   446
paulson@9840
   447
(** Best-first search versions **)
paulson@9840
   448
paulson@16563
   449
(*ths is a list of additional clauses (HOL disjunctions) to use.*)
wenzelm@9869
   450
fun best_meson_tac sizef =
wenzelm@9869
   451
  MESON (fn cls =>
paulson@9840
   452
         THEN_BEST_FIRST (resolve_tac (gocls cls) 1)
paulson@9840
   453
                         (has_fewer_prems 1, sizef)
paulson@9840
   454
                         (prolog_step_tac (make_horns cls) 1));
paulson@9840
   455
paulson@9840
   456
(*First, breaks the goal into independent units*)
paulson@9840
   457
val safe_best_meson_tac =
wenzelm@9869
   458
     SELECT_GOAL (TRY Safe_tac THEN
paulson@9840
   459
                  TRYALL (best_meson_tac size_of_subgoals));
paulson@9840
   460
paulson@9840
   461
(** Depth-first search version **)
paulson@9840
   462
paulson@9840
   463
val depth_meson_tac =
wenzelm@9869
   464
     MESON (fn cls => EVERY [resolve_tac (gocls cls) 1,
paulson@9840
   465
                             depth_prolog_tac (make_horns cls)]);
paulson@9840
   466
paulson@9840
   467
paulson@9840
   468
(** Iterative deepening version **)
paulson@9840
   469
paulson@9840
   470
(*This version does only one inference per call;
paulson@9840
   471
  having only one eq_assume_tac speeds it up!*)
wenzelm@9869
   472
fun prolog_step_tac' horns =
paulson@9840
   473
    let val (horn0s, hornps) = (*0 subgoals vs 1 or more*)
paulson@9840
   474
            take_prefix Thm.no_prems horns
paulson@9840
   475
        val nrtac = net_resolve_tac horns
paulson@9840
   476
    in  fn i => eq_assume_tac i ORELSE
paulson@9840
   477
                match_tac horn0s i ORELSE  (*no backtracking if unit MATCHES*)
paulson@9840
   478
                ((assume_tac i APPEND nrtac i) THEN check_tac)
paulson@9840
   479
    end;
paulson@9840
   480
wenzelm@9869
   481
fun iter_deepen_prolog_tac horns =
paulson@9840
   482
    ITER_DEEPEN (has_fewer_prems 1) (prolog_step_tac' horns);
paulson@9840
   483
paulson@16563
   484
fun iter_deepen_meson_tac ths =
wenzelm@9869
   485
  MESON (fn cls =>
paulson@16563
   486
           case (gocls (cls@ths)) of
paulson@16563
   487
           	[] => no_tac  (*no goal clauses*)
paulson@16563
   488
              | goes => 
paulson@16563
   489
		 (THEN_ITER_DEEPEN (resolve_tac goes 1)
paulson@16563
   490
				   (has_fewer_prems 1)
paulson@16563
   491
				   (prolog_step_tac' (make_horns (cls@ths)))));
paulson@9840
   492
paulson@16563
   493
fun meson_claset_tac ths cs =
paulson@16563
   494
  SELECT_GOAL (TRY (safe_tac cs) THEN TRYALL (iter_deepen_meson_tac ths));
wenzelm@9869
   495
paulson@16563
   496
val meson_tac = CLASET' (meson_claset_tac []);
wenzelm@9869
   497
wenzelm@9869
   498
paulson@14813
   499
(**** Code to support ordinary resolution, rather than Model Elimination ****)
paulson@14744
   500
paulson@15008
   501
(*Convert a list of clauses (disjunctions) to meta-level clauses (==>), 
paulson@15008
   502
  with no contrapositives, for ordinary resolution.*)
paulson@14744
   503
paulson@14744
   504
(*Rules to convert the head literal into a negated assumption. If the head
paulson@14744
   505
  literal is already negated, then using notEfalse instead of notEfalse'
paulson@14744
   506
  prevents a double negation.*)
paulson@14744
   507
val notEfalse = read_instantiate [("R","False")] notE;
paulson@14744
   508
val notEfalse' = rotate_prems 1 notEfalse;
paulson@14744
   509
paulson@15448
   510
fun negated_asm_of_head th = 
paulson@14744
   511
    th RS notEfalse handle THM _ => th RS notEfalse';
paulson@14744
   512
paulson@14744
   513
(*Converting one clause*)
paulson@15581
   514
fun make_meta_clause th = 
paulson@16588
   515
    negated_asm_of_head (make_horn resolution_clause_rules (check_is_fol th));
paulson@14744
   516
paulson@14744
   517
fun make_meta_clauses ths =
paulson@14744
   518
    name_thms "MClause#"
wenzelm@19046
   519
      (distinct Drule.eq_thm_prop (map make_meta_clause ths));
paulson@14744
   520
paulson@14744
   521
(*Permute a rule's premises to move the i-th premise to the last position.*)
paulson@14744
   522
fun make_last i th =
paulson@14744
   523
  let val n = nprems_of th 
paulson@14744
   524
  in  if 1 <= i andalso i <= n 
paulson@14744
   525
      then Thm.permute_prems (i-1) 1 th
paulson@15118
   526
      else raise THM("select_literal", i, [th])
paulson@14744
   527
  end;
paulson@14744
   528
paulson@14744
   529
(*Maps a rule that ends "... ==> P ==> False" to "... ==> ~P" while suppressing
paulson@14744
   530
  double-negations.*)
paulson@14744
   531
val negate_head = rewrite_rule [atomize_not, not_not RS eq_reflection];
paulson@14744
   532
paulson@14744
   533
(*Maps the clause  [P1,...Pn]==>False to [P1,...,P(i-1),P(i+1),...Pn] ==> ~P*)
paulson@14744
   534
fun select_literal i cl = negate_head (make_last i cl);
paulson@14744
   535
paulson@18508
   536
paulson@14813
   537
(*Top-level Skolemization. Allows part of the conversion to clauses to be
paulson@14813
   538
  expressed as a tactic (or Isar method).  Each assumption of the selected 
paulson@14813
   539
  goal is converted to NNF and then its existential quantifiers are pulled
paulson@14813
   540
  to the front. Finally, all existential quantifiers are eliminated, 
paulson@14813
   541
  leaving !!-quantified variables. Perhaps Safe_tac should follow, but it
paulson@14813
   542
  might generate many subgoals.*)
mengj@18194
   543
paulson@19204
   544
fun skolemize_tac i st = 
paulson@19204
   545
  let val ts = Logic.strip_assums_hyp (List.nth (prems_of st, i-1))
paulson@19204
   546
  in 
paulson@19204
   547
     EVERY' [METAHYPS
quigley@15773
   548
	    (fn hyps => (cut_facts_tac (map (skolemize o make_nnf) hyps) 1
paulson@14813
   549
                         THEN REPEAT (etac exE 1))),
paulson@19204
   550
            REPEAT_DETERM_N (length ts) o (etac thin_rl)] i st
paulson@19204
   551
  end
paulson@19204
   552
  handle Subscript => Seq.empty;
mengj@18194
   553
paulson@15118
   554
(*Top-level conversion to meta-level clauses. Each clause has  
paulson@15118
   555
  leading !!-bound universal variables, to express generality. To get 
paulson@15118
   556
  disjunctions instead of meta-clauses, remove "make_meta_clauses" below.*)
paulson@15008
   557
val make_clauses_tac = 
paulson@15008
   558
  SUBGOAL
paulson@15008
   559
    (fn (prop,_) =>
paulson@15008
   560
     let val ts = Logic.strip_assums_hyp prop
paulson@15008
   561
     in EVERY1 
paulson@15008
   562
	 [METAHYPS
paulson@15008
   563
	    (fn hyps => 
paulson@15151
   564
              (Method.insert_tac
paulson@15118
   565
                (map forall_intr_vars 
paulson@15118
   566
                  (make_meta_clauses (make_clauses hyps))) 1)),
paulson@15008
   567
	  REPEAT_DETERM_N (length ts) o (etac thin_rl)]
paulson@15008
   568
     end);
paulson@16563
   569
     
paulson@16563
   570
     
paulson@16563
   571
(*** setup the special skoklemization methods ***)
wenzelm@9869
   572
paulson@16563
   573
(*No CHANGED_PROP here, since these always appear in the preamble*)
wenzelm@9869
   574
paulson@16563
   575
val skolemize_meth = Method.SIMPLE_METHOD' HEADGOAL skolemize_tac;
paulson@16563
   576
paulson@16563
   577
val make_clauses_meth = Method.SIMPLE_METHOD' HEADGOAL make_clauses_tac;
paulson@14890
   578
paulson@16563
   579
val skolemize_setup =
wenzelm@18708
   580
  Method.add_methods
wenzelm@18708
   581
    [("skolemize", Method.no_args skolemize_meth, 
wenzelm@18708
   582
      "Skolemization into existential quantifiers"),
wenzelm@18708
   583
     ("make_clauses", Method.no_args make_clauses_meth, 
wenzelm@18708
   584
      "Conversion to !!-quantified meta-level clauses")];
paulson@9840
   585
paulson@9840
   586
end;
wenzelm@9869
   587
paulson@15579
   588
structure BasicMeson: BASIC_MESON = Meson;
paulson@15579
   589
open BasicMeson;