src/HOL/Tools/meson.ML
author blanchet
Mon Mar 22 10:25:07 2010 +0100 (2010-03-22)
changeset 35869 cac366550624
parent 35625 9c818cab0dd0
child 35870 05f3af00cc7e
permissions -rw-r--r--
start work on direct proof reconstruction for Sledgehammer
wenzelm@9869
     1
(*  Title:      HOL/Tools/meson.ML
paulson@9840
     2
    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
paulson@9840
     3
wenzelm@9869
     4
The MESON resolution proof procedure for HOL.
wenzelm@29267
     5
When making clauses, avoids using the rewriter -- instead uses RS recursively.
paulson@9840
     6
*)
paulson@9840
     7
wenzelm@24300
     8
signature MESON =
paulson@15579
     9
sig
wenzelm@32955
    10
  val trace: bool Unsynchronized.ref
wenzelm@24300
    11
  val term_pair_of: indexname * (typ * 'a) -> term * 'a
wenzelm@24300
    12
  val first_order_resolve: thm -> thm -> thm
wenzelm@24300
    13
  val flexflex_first_order: thm -> thm
wenzelm@24300
    14
  val size_of_subgoals: thm -> int
paulson@26562
    15
  val too_many_clauses: Proof.context option -> term -> bool
paulson@24937
    16
  val make_cnf: thm list -> thm -> Proof.context -> thm list * Proof.context
wenzelm@24300
    17
  val finish_cnf: thm list -> thm list
wenzelm@32262
    18
  val make_nnf: Proof.context -> thm -> thm
wenzelm@32262
    19
  val skolemize: Proof.context -> thm -> thm
wenzelm@24300
    20
  val is_fol_term: theory -> term -> bool
blanchet@35869
    21
  val make_clauses_unsorted: thm list -> thm list
wenzelm@24300
    22
  val make_clauses: thm list -> thm list
wenzelm@24300
    23
  val make_horns: thm list -> thm list
wenzelm@24300
    24
  val best_prolog_tac: (thm -> int) -> thm list -> tactic
wenzelm@24300
    25
  val depth_prolog_tac: thm list -> tactic
wenzelm@24300
    26
  val gocls: thm list -> thm list
wenzelm@32262
    27
  val skolemize_prems_tac: Proof.context -> thm list -> int -> tactic
wenzelm@32262
    28
  val MESON: (thm list -> thm list) -> (thm list -> tactic) -> Proof.context -> int -> tactic
wenzelm@32262
    29
  val best_meson_tac: (thm -> int) -> Proof.context -> int -> tactic
wenzelm@32262
    30
  val safe_best_meson_tac: Proof.context -> int -> tactic
wenzelm@32262
    31
  val depth_meson_tac: Proof.context -> int -> tactic
wenzelm@24300
    32
  val prolog_step_tac': thm list -> int -> tactic
wenzelm@24300
    33
  val iter_deepen_prolog_tac: thm list -> tactic
wenzelm@32262
    34
  val iter_deepen_meson_tac: Proof.context -> thm list -> int -> tactic
wenzelm@24300
    35
  val make_meta_clause: thm -> thm
wenzelm@24300
    36
  val make_meta_clauses: thm list -> thm list
wenzelm@32262
    37
  val meson_tac: Proof.context -> thm list -> int -> tactic
wenzelm@24300
    38
  val negate_head: thm -> thm
wenzelm@24300
    39
  val select_literal: int -> thm -> thm
wenzelm@32262
    40
  val skolemize_tac: Proof.context -> int -> tactic
wenzelm@32262
    41
  val setup: theory -> theory
paulson@15579
    42
end
paulson@9840
    43
wenzelm@24300
    44
structure Meson: MESON =
paulson@15579
    45
struct
paulson@9840
    46
wenzelm@32955
    47
val trace = Unsynchronized.ref false;
wenzelm@32955
    48
fun trace_msg msg = if ! trace then tracing (msg ()) else ();
wenzelm@32955
    49
paulson@26562
    50
val max_clauses_default = 60;
paulson@26562
    51
val (max_clauses, setup) = Attrib.config_int "max_clauses" max_clauses_default;
paulson@26562
    52
haftmann@31454
    53
val disj_forward = @{thm disj_forward};
haftmann@31454
    54
val disj_forward2 = @{thm disj_forward2};
haftmann@31454
    55
val make_pos_rule = @{thm make_pos_rule};
haftmann@31454
    56
val make_pos_rule' = @{thm make_pos_rule'};
haftmann@31454
    57
val make_pos_goal = @{thm make_pos_goal};
haftmann@31454
    58
val make_neg_rule = @{thm make_neg_rule};
haftmann@31454
    59
val make_neg_rule' = @{thm make_neg_rule'};
haftmann@31454
    60
val make_neg_goal = @{thm make_neg_goal};
haftmann@31454
    61
val conj_forward = @{thm conj_forward};
haftmann@31454
    62
val all_forward = @{thm all_forward};
haftmann@31454
    63
val ex_forward = @{thm ex_forward};
haftmann@31454
    64
val choice = @{thm choice};
haftmann@31454
    65
paulson@15579
    66
val not_conjD = thm "meson_not_conjD";
paulson@15579
    67
val not_disjD = thm "meson_not_disjD";
paulson@15579
    68
val not_notD = thm "meson_not_notD";
paulson@15579
    69
val not_allD = thm "meson_not_allD";
paulson@15579
    70
val not_exD = thm "meson_not_exD";
paulson@15579
    71
val imp_to_disjD = thm "meson_imp_to_disjD";
paulson@15579
    72
val not_impD = thm "meson_not_impD";
paulson@15579
    73
val iff_to_disjD = thm "meson_iff_to_disjD";
paulson@15579
    74
val not_iffD = thm "meson_not_iffD";
paulson@15579
    75
val conj_exD1 = thm "meson_conj_exD1";
paulson@15579
    76
val conj_exD2 = thm "meson_conj_exD2";
paulson@15579
    77
val disj_exD = thm "meson_disj_exD";
paulson@15579
    78
val disj_exD1 = thm "meson_disj_exD1";
paulson@15579
    79
val disj_exD2 = thm "meson_disj_exD2";
paulson@15579
    80
val disj_assoc = thm "meson_disj_assoc";
paulson@15579
    81
val disj_comm = thm "meson_disj_comm";
paulson@15579
    82
val disj_FalseD1 = thm "meson_disj_FalseD1";
paulson@15579
    83
val disj_FalseD2 = thm "meson_disj_FalseD2";
paulson@9840
    84
paulson@9840
    85
paulson@15579
    86
(**** Operators for forward proof ****)
paulson@15579
    87
paulson@20417
    88
paulson@20417
    89
(** First-order Resolution **)
paulson@20417
    90
paulson@20417
    91
fun typ_pair_of (ix, (sort,ty)) = (TVar (ix,sort), ty);
paulson@20417
    92
fun term_pair_of (ix, (ty,t)) = (Var (ix,ty), t);
paulson@20417
    93
paulson@20417
    94
(*FIXME: currently does not "rename variables apart"*)
paulson@20417
    95
fun first_order_resolve thA thB =
wenzelm@32262
    96
  (case
wenzelm@32262
    97
    try (fn () =>
wenzelm@32262
    98
      let val thy = theory_of_thm thA
wenzelm@32262
    99
          val tmA = concl_of thA
wenzelm@32262
   100
          val Const("==>",_) $ tmB $ _ = prop_of thB
wenzelm@32262
   101
          val (tyenv, tenv) = Pattern.first_order_match thy (tmB, tmA) (Vartab.empty, Vartab.empty)
wenzelm@32262
   102
          val ct_pairs = map (pairself (cterm_of thy) o term_pair_of) (Vartab.dest tenv)
wenzelm@32262
   103
      in  thA RS (cterm_instantiate ct_pairs thB)  end) () of
wenzelm@32262
   104
    SOME th => th
wenzelm@32262
   105
  | NONE => raise THM ("first_order_resolve", 0, [thA, thB]));
paulson@18175
   106
wenzelm@24300
   107
fun flexflex_first_order th =
paulson@23440
   108
  case (tpairs_of th) of
paulson@23440
   109
      [] => th
paulson@23440
   110
    | pairs =>
wenzelm@24300
   111
        let val thy = theory_of_thm th
wenzelm@32032
   112
            val (tyenv, tenv) =
wenzelm@32032
   113
              fold (Pattern.first_order_match thy) pairs (Vartab.empty, Vartab.empty)
wenzelm@24300
   114
            val t_pairs = map term_pair_of (Vartab.dest tenv)
wenzelm@24300
   115
            val th' = Thm.instantiate ([], map (pairself (cterm_of thy)) t_pairs) th
wenzelm@24300
   116
        in  th'  end
wenzelm@24300
   117
        handle THM _ => th;
paulson@23440
   118
paulson@24937
   119
(*Forward proof while preserving bound variables names*)
paulson@24937
   120
fun rename_bvs_RS th rl =
paulson@24937
   121
  let val th' = th RS rl
paulson@24937
   122
  in  Thm.rename_boundvars (concl_of th') (concl_of th) th' end;
paulson@24937
   123
paulson@24937
   124
(*raises exception if no rules apply*)
wenzelm@24300
   125
fun tryres (th, rls) =
paulson@18141
   126
  let fun tryall [] = raise THM("tryres", 0, th::rls)
paulson@24937
   127
        | tryall (rl::rls) = (rename_bvs_RS th rl handle THM _ => tryall rls)
paulson@18141
   128
  in  tryall rls  end;
wenzelm@24300
   129
paulson@21050
   130
(*Permits forward proof from rules that discharge assumptions. The supplied proof state st,
paulson@21050
   131
  e.g. from conj_forward, should have the form
paulson@21050
   132
    "[| P' ==> ?P; Q' ==> ?Q |] ==> ?P & ?Q"
paulson@21050
   133
  and the effect should be to instantiate ?P and ?Q with normalized versions of P' and Q'.*)
wenzelm@32262
   134
fun forward_res ctxt nf st =
paulson@21050
   135
  let fun forward_tacf [prem] = rtac (nf prem) 1
wenzelm@24300
   136
        | forward_tacf prems =
wenzelm@32091
   137
            error (cat_lines
wenzelm@32091
   138
              ("Bad proof state in forward_res, please inform lcp@cl.cam.ac.uk:" ::
wenzelm@32262
   139
                Display.string_of_thm ctxt st ::
wenzelm@32262
   140
                "Premises:" :: map (Display.string_of_thm ctxt) prems))
paulson@21050
   141
  in
wenzelm@32231
   142
    case Seq.pull (ALLGOALS (OldGoals.METAHYPS forward_tacf) st)
paulson@21050
   143
    of SOME(th,_) => th
paulson@21050
   144
     | NONE => raise THM("forward_res", 0, [st])
paulson@21050
   145
  end;
paulson@15579
   146
paulson@20134
   147
(*Are any of the logical connectives in "bs" present in the term?*)
paulson@20134
   148
fun has_conns bs =
paulson@20134
   149
  let fun has (Const(a,_)) = false
paulson@20134
   150
        | has (Const("Trueprop",_) $ p) = has p
paulson@20134
   151
        | has (Const("Not",_) $ p) = has p
paulson@20134
   152
        | has (Const("op |",_) $ p $ q) = member (op =) bs "op |" orelse has p orelse has q
paulson@20134
   153
        | has (Const("op &",_) $ p $ q) = member (op =) bs "op &" orelse has p orelse has q
paulson@20134
   154
        | has (Const("All",_) $ Abs(_,_,p)) = member (op =) bs "All" orelse has p
paulson@20134
   155
        | has (Const("Ex",_) $ Abs(_,_,p)) = member (op =) bs "Ex" orelse has p
wenzelm@24300
   156
        | has _ = false
paulson@15579
   157
  in  has  end;
wenzelm@24300
   158
paulson@9840
   159
paulson@15579
   160
(**** Clause handling ****)
paulson@9840
   161
paulson@15579
   162
fun literals (Const("Trueprop",_) $ P) = literals P
paulson@15579
   163
  | literals (Const("op |",_) $ P $ Q) = literals P @ literals Q
paulson@15579
   164
  | literals (Const("Not",_) $ P) = [(false,P)]
paulson@15579
   165
  | literals P = [(true,P)];
paulson@9840
   166
paulson@15579
   167
(*number of literals in a term*)
paulson@15579
   168
val nliterals = length o literals;
paulson@9840
   169
paulson@18389
   170
paulson@18389
   171
(*** Tautology Checking ***)
paulson@18389
   172
wenzelm@24300
   173
fun signed_lits_aux (Const ("op |", _) $ P $ Q) (poslits, neglits) =
paulson@18389
   174
      signed_lits_aux Q (signed_lits_aux P (poslits, neglits))
paulson@18389
   175
  | signed_lits_aux (Const("Not",_) $ P) (poslits, neglits) = (poslits, P::neglits)
paulson@18389
   176
  | signed_lits_aux P (poslits, neglits) = (P::poslits, neglits);
wenzelm@24300
   177
paulson@18389
   178
fun signed_lits th = signed_lits_aux (HOLogic.dest_Trueprop (concl_of th)) ([],[]);
paulson@18389
   179
paulson@18389
   180
(*Literals like X=X are tautologous*)
paulson@18389
   181
fun taut_poslit (Const("op =",_) $ t $ u) = t aconv u
paulson@18389
   182
  | taut_poslit (Const("True",_)) = true
paulson@18389
   183
  | taut_poslit _ = false;
paulson@18389
   184
paulson@18389
   185
fun is_taut th =
paulson@18389
   186
  let val (poslits,neglits) = signed_lits th
paulson@18389
   187
  in  exists taut_poslit poslits
paulson@18389
   188
      orelse
wenzelm@20073
   189
      exists (member (op aconv) neglits) (HOLogic.false_const :: poslits)
paulson@19894
   190
  end
wenzelm@24300
   191
  handle TERM _ => false;       (*probably dest_Trueprop on a weird theorem*)
paulson@18389
   192
paulson@18389
   193
paulson@18389
   194
(*** To remove trivial negated equality literals from clauses ***)
paulson@18389
   195
paulson@18389
   196
(*They are typically functional reflexivity axioms and are the converses of
paulson@18389
   197
  injectivity equivalences*)
wenzelm@24300
   198
paulson@18389
   199
val not_refl_disj_D = thm"meson_not_refl_disj_D";
paulson@18389
   200
paulson@20119
   201
(*Is either term a Var that does not properly occur in the other term?*)
paulson@20119
   202
fun eliminable (t as Var _, u) = t aconv u orelse not (Logic.occs(t,u))
paulson@20119
   203
  | eliminable (u, t as Var _) = t aconv u orelse not (Logic.occs(t,u))
paulson@20119
   204
  | eliminable _ = false;
paulson@20119
   205
paulson@18389
   206
fun refl_clause_aux 0 th = th
paulson@18389
   207
  | refl_clause_aux n th =
paulson@18389
   208
       case HOLogic.dest_Trueprop (concl_of th) of
wenzelm@24300
   209
          (Const ("op |", _) $ (Const ("op |", _) $ _ $ _) $ _) =>
paulson@18389
   210
            refl_clause_aux n (th RS disj_assoc)    (*isolate an atom as first disjunct*)
wenzelm@24300
   211
        | (Const ("op |", _) $ (Const("Not",_) $ (Const("op =",_) $ t $ u)) $ _) =>
wenzelm@24300
   212
            if eliminable(t,u)
wenzelm@24300
   213
            then refl_clause_aux (n-1) (th RS not_refl_disj_D)  (*Var inequation: delete*)
wenzelm@24300
   214
            else refl_clause_aux (n-1) (th RS disj_comm)  (*not between Vars: ignore*)
wenzelm@24300
   215
        | (Const ("op |", _) $ _ $ _) => refl_clause_aux n (th RS disj_comm)
wenzelm@24300
   216
        | _ => (*not a disjunction*) th;
paulson@18389
   217
wenzelm@24300
   218
fun notequal_lits_count (Const ("op |", _) $ P $ Q) =
paulson@18389
   219
      notequal_lits_count P + notequal_lits_count Q
paulson@18389
   220
  | notequal_lits_count (Const("Not",_) $ (Const("op =",_) $ _ $ _)) = 1
paulson@18389
   221
  | notequal_lits_count _ = 0;
paulson@18389
   222
paulson@18389
   223
(*Simplify a clause by applying reflexivity to its negated equality literals*)
wenzelm@24300
   224
fun refl_clause th =
paulson@18389
   225
  let val neqs = notequal_lits_count (HOLogic.dest_Trueprop (concl_of th))
paulson@19894
   226
  in  zero_var_indexes (refl_clause_aux neqs th)  end
wenzelm@24300
   227
  handle TERM _ => th;  (*probably dest_Trueprop on a weird theorem*)
paulson@18389
   228
paulson@18389
   229
paulson@24937
   230
(*** Removal of duplicate literals ***)
paulson@24937
   231
paulson@24937
   232
(*Forward proof, passing extra assumptions as theorems to the tactic*)
wenzelm@32262
   233
fun forward_res2 ctxt nf hyps st =
paulson@24937
   234
  case Seq.pull
paulson@24937
   235
        (REPEAT
wenzelm@32231
   236
         (OldGoals.METAHYPS (fn major::minors => rtac (nf (minors@hyps) major) 1) 1)
paulson@24937
   237
         st)
paulson@24937
   238
  of SOME(th,_) => th
paulson@24937
   239
   | NONE => raise THM("forward_res2", 0, [st]);
paulson@24937
   240
paulson@24937
   241
(*Remove duplicates in P|Q by assuming ~P in Q
paulson@24937
   242
  rls (initially []) accumulates assumptions of the form P==>False*)
wenzelm@32262
   243
fun nodups_aux ctxt rls th = nodups_aux ctxt rls (th RS disj_assoc)
paulson@24937
   244
    handle THM _ => tryres(th,rls)
wenzelm@32262
   245
    handle THM _ => tryres(forward_res2 ctxt (nodups_aux ctxt) rls (th RS disj_forward2),
paulson@24937
   246
                           [disj_FalseD1, disj_FalseD2, asm_rl])
paulson@24937
   247
    handle THM _ => th;
paulson@24937
   248
paulson@24937
   249
(*Remove duplicate literals, if there are any*)
wenzelm@32262
   250
fun nodups ctxt th =
paulson@24937
   251
  if has_duplicates (op =) (literals (prop_of th))
wenzelm@32262
   252
    then nodups_aux ctxt [] th
paulson@24937
   253
    else th;
paulson@24937
   254
paulson@24937
   255
paulson@18389
   256
(*** The basic CNF transformation ***)
paulson@18389
   257
paulson@26562
   258
fun too_many_clauses ctxto t = 
paulson@26562
   259
 let
paulson@26562
   260
  val max_cl = case ctxto of SOME ctxt => Config.get ctxt max_clauses
paulson@26562
   261
                           | NONE => max_clauses_default
paulson@26562
   262
  
paulson@26562
   263
  fun sum x y = if x < max_cl andalso y < max_cl then x+y else max_cl;
paulson@26562
   264
  fun prod x y = if x < max_cl andalso y < max_cl then x*y else max_cl;
paulson@26562
   265
  
paulson@26562
   266
  (*Estimate the number of clauses in order to detect infeasible theorems*)
paulson@26562
   267
  fun signed_nclauses b (Const("Trueprop",_) $ t) = signed_nclauses b t
paulson@26562
   268
    | signed_nclauses b (Const("Not",_) $ t) = signed_nclauses (not b) t
paulson@26562
   269
    | signed_nclauses b (Const("op &",_) $ t $ u) =
wenzelm@32960
   270
        if b then sum (signed_nclauses b t) (signed_nclauses b u)
wenzelm@32960
   271
             else prod (signed_nclauses b t) (signed_nclauses b u)
paulson@26562
   272
    | signed_nclauses b (Const("op |",_) $ t $ u) =
wenzelm@32960
   273
        if b then prod (signed_nclauses b t) (signed_nclauses b u)
wenzelm@32960
   274
             else sum (signed_nclauses b t) (signed_nclauses b u)
paulson@26562
   275
    | signed_nclauses b (Const("op -->",_) $ t $ u) =
wenzelm@32960
   276
        if b then prod (signed_nclauses (not b) t) (signed_nclauses b u)
wenzelm@32960
   277
             else sum (signed_nclauses (not b) t) (signed_nclauses b u)
paulson@26562
   278
    | signed_nclauses b (Const("op =", Type ("fun", [T, _])) $ t $ u) =
wenzelm@32960
   279
        if T = HOLogic.boolT then (*Boolean equality is if-and-only-if*)
wenzelm@32960
   280
            if b then sum (prod (signed_nclauses (not b) t) (signed_nclauses b u))
wenzelm@32960
   281
                          (prod (signed_nclauses (not b) u) (signed_nclauses b t))
wenzelm@32960
   282
                 else sum (prod (signed_nclauses b t) (signed_nclauses b u))
wenzelm@32960
   283
                          (prod (signed_nclauses (not b) t) (signed_nclauses (not b) u))
wenzelm@32960
   284
        else 1
paulson@26562
   285
    | signed_nclauses b (Const("Ex", _) $ Abs (_,_,t)) = signed_nclauses b t
paulson@26562
   286
    | signed_nclauses b (Const("All",_) $ Abs (_,_,t)) = signed_nclauses b t
paulson@26562
   287
    | signed_nclauses _ _ = 1; (* literal *)
paulson@26562
   288
 in 
paulson@26562
   289
  signed_nclauses true t >= max_cl
paulson@26562
   290
 end;
paulson@19894
   291
paulson@15579
   292
(*Replaces universally quantified variables by FREE variables -- because
paulson@24937
   293
  assumptions may not contain scheme variables.  Later, generalize using Variable.export. *)
paulson@24937
   294
local  
paulson@24937
   295
  val spec_var = Thm.dest_arg (Thm.dest_arg (#2 (Thm.dest_implies (Thm.cprop_of spec))));
paulson@24937
   296
  val spec_varT = #T (Thm.rep_cterm spec_var);
paulson@24937
   297
  fun name_of (Const ("All", _) $ Abs(x,_,_)) = x | name_of _ = Name.uu;
paulson@24937
   298
in  
paulson@24937
   299
  fun freeze_spec th ctxt =
paulson@24937
   300
    let
paulson@24937
   301
      val cert = Thm.cterm_of (ProofContext.theory_of ctxt);
paulson@24937
   302
      val ([x], ctxt') = Variable.variant_fixes [name_of (HOLogic.dest_Trueprop (concl_of th))] ctxt;
paulson@24937
   303
      val spec' = Thm.instantiate ([], [(spec_var, cert (Free (x, spec_varT)))]) spec;
paulson@24937
   304
    in (th RS spec', ctxt') end
paulson@24937
   305
end;
paulson@9840
   306
paulson@15998
   307
(*Used with METAHYPS below. There is one assumption, which gets bound to prem
paulson@15998
   308
  and then normalized via function nf. The normal form is given to resolve_tac,
paulson@22515
   309
  instantiate a Boolean variable created by resolution with disj_forward. Since
paulson@22515
   310
  (nf prem) returns a LIST of theorems, we can backtrack to get all combinations.*)
paulson@15579
   311
fun resop nf [prem] = resolve_tac (nf prem) 1;
paulson@9840
   312
wenzelm@24300
   313
(*Any need to extend this list with
wenzelm@26424
   314
  "HOL.type_class","HOL.eq_class","Pure.term"?*)
wenzelm@24300
   315
val has_meta_conn =
paulson@29684
   316
    exists_Const (member (op =) ["==", "==>", "=simp=>", "all", "prop"] o #1);
paulson@20417
   317
wenzelm@24300
   318
fun apply_skolem_ths (th, rls) =
paulson@20417
   319
  let fun tryall [] = raise THM("apply_skolem_ths", 0, th::rls)
paulson@20417
   320
        | tryall (rl::rls) = (first_order_resolve th rl handle THM _ => tryall rls)
paulson@20417
   321
  in  tryall rls  end;
paulson@22515
   322
paulson@15998
   323
(*Conjunctive normal form, adding clauses from th in front of ths (for foldr).
paulson@15998
   324
  Strips universal quantifiers and breaks up conjunctions.
paulson@15998
   325
  Eliminates existential quantifiers using skoths: Skolemization theorems.*)
paulson@24937
   326
fun cnf skoths ctxt (th,ths) =
wenzelm@33222
   327
  let val ctxtr = Unsynchronized.ref ctxt   (* FIXME ??? *)
paulson@24937
   328
      fun cnf_aux (th,ths) =
wenzelm@24300
   329
        if not (can HOLogic.dest_Trueprop (prop_of th)) then ths (*meta-level: ignore*)
wenzelm@24300
   330
        else if not (has_conns ["All","Ex","op &"] (prop_of th))
wenzelm@32262
   331
        then nodups ctxt th :: ths (*no work to do, terminate*)
wenzelm@24300
   332
        else case head_of (HOLogic.dest_Trueprop (concl_of th)) of
wenzelm@24300
   333
            Const ("op &", _) => (*conjunction*)
wenzelm@24300
   334
                cnf_aux (th RS conjunct1, cnf_aux (th RS conjunct2, ths))
wenzelm@24300
   335
          | Const ("All", _) => (*universal quantifier*)
paulson@24937
   336
                let val (th',ctxt') = freeze_spec th (!ctxtr)
paulson@24937
   337
                in  ctxtr := ctxt'; cnf_aux (th', ths) end
wenzelm@24300
   338
          | Const ("Ex", _) =>
wenzelm@24300
   339
              (*existential quantifier: Insert Skolem functions*)
wenzelm@24300
   340
              cnf_aux (apply_skolem_ths (th,skoths), ths)
wenzelm@24300
   341
          | Const ("op |", _) =>
wenzelm@24300
   342
              (*Disjunction of P, Q: Create new goal of proving ?P | ?Q and solve it using
wenzelm@24300
   343
                all combinations of converting P, Q to CNF.*)
wenzelm@24300
   344
              let val tac =
wenzelm@32262
   345
                  OldGoals.METAHYPS (resop cnf_nil) 1 THEN
wenzelm@32231
   346
                   (fn st' => st' |> OldGoals.METAHYPS (resop cnf_nil) 1)
wenzelm@24300
   347
              in  Seq.list_of (tac (th RS disj_forward)) @ ths  end
wenzelm@32262
   348
          | _ => nodups ctxt th :: ths  (*no work to do*)
paulson@19154
   349
      and cnf_nil th = cnf_aux (th,[])
paulson@24937
   350
      val cls = 
wenzelm@32960
   351
            if too_many_clauses (SOME ctxt) (concl_of th)
wenzelm@32960
   352
            then (trace_msg (fn () => "cnf is ignoring: " ^ Display.string_of_thm ctxt th); ths)
wenzelm@32960
   353
            else cnf_aux (th,ths)
paulson@24937
   354
  in  (cls, !ctxtr)  end;
paulson@22515
   355
paulson@24937
   356
fun make_cnf skoths th ctxt = cnf skoths ctxt (th, []);
paulson@20417
   357
paulson@20417
   358
(*Generalization, removal of redundant equalities, removal of tautologies.*)
paulson@24937
   359
fun finish_cnf ths = filter (not o is_taut) (map refl_clause ths);
paulson@9840
   360
paulson@9840
   361
paulson@15579
   362
(**** Generation of contrapositives ****)
paulson@9840
   363
wenzelm@24300
   364
fun is_left (Const ("Trueprop", _) $
paulson@21102
   365
               (Const ("op |", _) $ (Const ("op |", _) $ _ $ _) $ _)) = true
paulson@21102
   366
  | is_left _ = false;
wenzelm@24300
   367
paulson@15579
   368
(*Associate disjuctions to right -- make leftmost disjunct a LITERAL*)
wenzelm@24300
   369
fun assoc_right th =
paulson@21102
   370
  if is_left (prop_of th) then assoc_right (th RS disj_assoc)
paulson@21102
   371
  else th;
paulson@9840
   372
paulson@15579
   373
(*Must check for negative literal first!*)
paulson@15579
   374
val clause_rules = [disj_assoc, make_neg_rule, make_pos_rule];
paulson@9840
   375
paulson@15579
   376
(*For ordinary resolution. *)
paulson@15579
   377
val resolution_clause_rules = [disj_assoc, make_neg_rule', make_pos_rule'];
paulson@9840
   378
paulson@15579
   379
(*Create a goal or support clause, conclusing False*)
paulson@15579
   380
fun make_goal th =   (*Must check for negative literal first!*)
paulson@15579
   381
    make_goal (tryres(th, clause_rules))
paulson@15579
   382
  handle THM _ => tryres(th, [make_neg_goal, make_pos_goal]);
paulson@9840
   383
paulson@15579
   384
(*Sort clauses by number of literals*)
paulson@15579
   385
fun fewerlits(th1,th2) = nliterals(prop_of th1) < nliterals(prop_of th2);
paulson@9840
   386
paulson@18389
   387
fun sort_clauses ths = sort (make_ord fewerlits) ths;
paulson@9840
   388
paulson@15581
   389
(*True if the given type contains bool anywhere*)
paulson@15581
   390
fun has_bool (Type("bool",_)) = true
paulson@15581
   391
  | has_bool (Type(_, Ts)) = exists has_bool Ts
paulson@15581
   392
  | has_bool _ = false;
wenzelm@24300
   393
wenzelm@24300
   394
(*Is the string the name of a connective? Really only | and Not can remain,
wenzelm@24300
   395
  since this code expects to be called on a clause form.*)
wenzelm@19875
   396
val is_conn = member (op =)
wenzelm@24300
   397
    ["Trueprop", "op &", "op |", "op -->", "Not",
paulson@15613
   398
     "All", "Ex", "Ball", "Bex"];
paulson@15613
   399
wenzelm@24300
   400
(*True if the term contains a function--not a logical connective--where the type
paulson@20524
   401
  of any argument contains bool.*)
wenzelm@24300
   402
val has_bool_arg_const =
paulson@15613
   403
    exists_Const
paulson@15613
   404
      (fn (c,T) => not(is_conn c) andalso exists (has_bool) (binder_types T));
paulson@22381
   405
wenzelm@24300
   406
(*A higher-order instance of a first-order constant? Example is the definition of
haftmann@34974
   407
  one, 1, at a function type in theory SetsAndFunctions.*)
wenzelm@24300
   408
fun higher_inst_const thy (c,T) =
paulson@22381
   409
  case binder_types T of
paulson@22381
   410
      [] => false (*not a function type, OK*)
paulson@22381
   411
    | Ts => length (binder_types (Sign.the_const_type thy c)) <> length Ts;
paulson@22381
   412
paulson@24742
   413
(*Returns false if any Vars in the theorem mention type bool.
paulson@21102
   414
  Also rejects functions whose arguments are Booleans or other functions.*)
paulson@22381
   415
fun is_fol_term thy t =
paulson@22381
   416
    Term.is_first_order ["all","All","Ex"] t andalso
wenzelm@29267
   417
    not (exists_subterm (fn Var (_, T) => has_bool T | _ => false) t  orelse
wenzelm@24300
   418
         has_bool_arg_const t  orelse
wenzelm@24300
   419
         exists_Const (higher_inst_const thy) t orelse
wenzelm@24300
   420
         has_meta_conn t);
paulson@19204
   421
paulson@21102
   422
fun rigid t = not (is_Var (head_of t));
paulson@21102
   423
paulson@21102
   424
fun ok4horn (Const ("Trueprop",_) $ (Const ("op |", _) $ t $ _)) = rigid t
paulson@21102
   425
  | ok4horn (Const ("Trueprop",_) $ t) = rigid t
paulson@21102
   426
  | ok4horn _ = false;
paulson@21102
   427
paulson@15579
   428
(*Create a meta-level Horn clause*)
wenzelm@24300
   429
fun make_horn crules th =
wenzelm@24300
   430
  if ok4horn (concl_of th)
paulson@21102
   431
  then make_horn crules (tryres(th,crules)) handle THM _ => th
paulson@21102
   432
  else th;
paulson@9840
   433
paulson@16563
   434
(*Generate Horn clauses for all contrapositives of a clause. The input, th,
paulson@16563
   435
  is a HOL disjunction.*)
wenzelm@33339
   436
fun add_contras crules th hcs =
paulson@15579
   437
  let fun rots (0,th) = hcs
wenzelm@24300
   438
        | rots (k,th) = zero_var_indexes (make_horn crules th) ::
wenzelm@24300
   439
                        rots(k-1, assoc_right (th RS disj_comm))
paulson@15862
   440
  in case nliterals(prop_of th) of
wenzelm@24300
   441
        1 => th::hcs
paulson@15579
   442
      | n => rots(n, assoc_right th)
paulson@15579
   443
  end;
paulson@9840
   444
paulson@15579
   445
(*Use "theorem naming" to label the clauses*)
paulson@15579
   446
fun name_thms label =
wenzelm@33339
   447
    let fun name1 th (k, ths) =
wenzelm@27865
   448
          (k-1, Thm.put_name_hint (label ^ string_of_int k) th :: ths)
wenzelm@33339
   449
    in  fn ths => #2 (fold_rev name1 ths (length ths, []))  end;
paulson@9840
   450
paulson@16563
   451
(*Is the given disjunction an all-negative support clause?*)
paulson@15579
   452
fun is_negative th = forall (not o #1) (literals (prop_of th));
paulson@9840
   453
wenzelm@33317
   454
val neg_clauses = filter is_negative;
paulson@9840
   455
paulson@9840
   456
paulson@15579
   457
(***** MESON PROOF PROCEDURE *****)
paulson@9840
   458
paulson@15579
   459
fun rhyps (Const("==>",_) $ (Const("Trueprop",_) $ A) $ phi,
wenzelm@24300
   460
           As) = rhyps(phi, A::As)
paulson@15579
   461
  | rhyps (_, As) = As;
paulson@9840
   462
paulson@15579
   463
(** Detecting repeated assumptions in a subgoal **)
paulson@9840
   464
paulson@15579
   465
(*The stringtree detects repeated assumptions.*)
wenzelm@33245
   466
fun ins_term t net = Net.insert_term (op aconv) (t, t) net;
paulson@9840
   467
paulson@15579
   468
(*detects repetitions in a list of terms*)
paulson@15579
   469
fun has_reps [] = false
paulson@15579
   470
  | has_reps [_] = false
paulson@15579
   471
  | has_reps [t,u] = (t aconv u)
wenzelm@33245
   472
  | has_reps ts = (fold ins_term ts Net.empty; false) handle Net.INSERT => true;
paulson@9840
   473
paulson@15579
   474
(*Like TRYALL eq_assume_tac, but avoids expensive THEN calls*)
paulson@18508
   475
fun TRYING_eq_assume_tac 0 st = Seq.single st
paulson@18508
   476
  | TRYING_eq_assume_tac i st =
wenzelm@31945
   477
       TRYING_eq_assume_tac (i-1) (Thm.eq_assumption i st)
paulson@18508
   478
       handle THM _ => TRYING_eq_assume_tac (i-1) st;
paulson@18508
   479
paulson@18508
   480
fun TRYALL_eq_assume_tac st = TRYING_eq_assume_tac (nprems_of st) st;
paulson@9840
   481
paulson@15579
   482
(*Loop checking: FAIL if trying to prove the same thing twice
paulson@15579
   483
  -- if *ANY* subgoal has repeated literals*)
paulson@15579
   484
fun check_tac st =
paulson@15579
   485
  if exists (fn prem => has_reps (rhyps(prem,[]))) (prems_of st)
paulson@15579
   486
  then  Seq.empty  else  Seq.single st;
paulson@9840
   487
paulson@9840
   488
paulson@15579
   489
(* net_resolve_tac actually made it slower... *)
paulson@15579
   490
fun prolog_step_tac horns i =
paulson@15579
   491
    (assume_tac i APPEND resolve_tac horns i) THEN check_tac THEN
paulson@18508
   492
    TRYALL_eq_assume_tac;
paulson@9840
   493
paulson@9840
   494
(*Sums the sizes of the subgoals, ignoring hypotheses (ancestors)*)
wenzelm@33339
   495
fun addconcl prem sz = size_of_term (Logic.strip_assums_concl prem) + sz;
paulson@15579
   496
wenzelm@33339
   497
fun size_of_subgoals st = fold_rev addconcl (prems_of st) 0;
paulson@15579
   498
paulson@9840
   499
paulson@9840
   500
(*Negation Normal Form*)
paulson@9840
   501
val nnf_rls = [imp_to_disjD, iff_to_disjD, not_conjD, not_disjD,
wenzelm@9869
   502
               not_impD, not_iffD, not_allD, not_exD, not_notD];
paulson@15581
   503
paulson@21102
   504
fun ok4nnf (Const ("Trueprop",_) $ (Const ("Not", _) $ t)) = rigid t
paulson@21102
   505
  | ok4nnf (Const ("Trueprop",_) $ t) = rigid t
paulson@21102
   506
  | ok4nnf _ = false;
paulson@21102
   507
wenzelm@32262
   508
fun make_nnf1 ctxt th =
wenzelm@24300
   509
  if ok4nnf (concl_of th)
wenzelm@32262
   510
  then make_nnf1 ctxt (tryres(th, nnf_rls))
paulson@28174
   511
    handle THM ("tryres", _, _) =>
wenzelm@32262
   512
        forward_res ctxt (make_nnf1 ctxt)
wenzelm@9869
   513
           (tryres(th, [conj_forward,disj_forward,all_forward,ex_forward]))
paulson@28174
   514
    handle THM ("tryres", _, _) => th
paulson@21102
   515
  else th;
paulson@9840
   516
wenzelm@24300
   517
(*The simplification removes defined quantifiers and occurrences of True and False.
paulson@20018
   518
  nnf_ss also includes the one-point simprocs,
paulson@18405
   519
  which are needed to avoid the various one-point theorems from generating junk clauses.*)
paulson@19894
   520
val nnf_simps =
wenzelm@35410
   521
  [@{thm simp_implies_def}, @{thm Ex1_def}, @{thm Ball_def},@{thm  Bex_def}, @{thm if_True},
wenzelm@35410
   522
    @{thm if_False}, @{thm if_cancel}, @{thm if_eq_cancel}, @{thm cases_simp}];
paulson@19894
   523
val nnf_extra_simps =
wenzelm@35410
   524
  @{thms split_ifs} @ @{thms ex_simps} @ @{thms all_simps} @ @{thms simp_thms};
paulson@18405
   525
paulson@18405
   526
val nnf_ss =
wenzelm@24300
   527
  HOL_basic_ss addsimps nnf_extra_simps
wenzelm@24040
   528
    addsimprocs [defALL_regroup,defEX_regroup, @{simproc neq}, @{simproc let_simp}];
paulson@15872
   529
wenzelm@32262
   530
fun make_nnf ctxt th = case prems_of th of
paulson@21050
   531
    [] => th |> rewrite_rule (map safe_mk_meta_eq nnf_simps)
wenzelm@24300
   532
             |> simplify nnf_ss
wenzelm@32262
   533
             |> make_nnf1 ctxt
paulson@21050
   534
  | _ => raise THM ("make_nnf: premises in argument", 0, [th]);
paulson@15581
   535
paulson@15965
   536
(*Pull existential quantifiers to front. This accomplishes Skolemization for
paulson@15965
   537
  clauses that arise from a subgoal.*)
wenzelm@32262
   538
fun skolemize1 ctxt th =
paulson@20134
   539
  if not (has_conns ["Ex"] (prop_of th)) then th
wenzelm@32262
   540
  else (skolemize1 ctxt (tryres(th, [choice, conj_exD1, conj_exD2,
quigley@15679
   541
                              disj_exD, disj_exD1, disj_exD2])))
paulson@28174
   542
    handle THM ("tryres", _, _) =>
wenzelm@32262
   543
        skolemize1 ctxt (forward_res ctxt (skolemize1 ctxt)
wenzelm@9869
   544
                   (tryres (th, [conj_forward, disj_forward, all_forward])))
paulson@28174
   545
    handle THM ("tryres", _, _) => 
wenzelm@32262
   546
        forward_res ctxt (skolemize1 ctxt) (rename_bvs_RS th ex_forward);
paulson@29684
   547
wenzelm@32262
   548
fun skolemize ctxt th = skolemize1 ctxt (make_nnf ctxt th);
paulson@9840
   549
wenzelm@32262
   550
fun skolemize_nnf_list _ [] = []
wenzelm@32262
   551
  | skolemize_nnf_list ctxt (th::ths) =
wenzelm@32262
   552
      skolemize ctxt th :: skolemize_nnf_list ctxt ths
paulson@25710
   553
      handle THM _ => (*RS can fail if Unify.search_bound is too small*)
wenzelm@32955
   554
       (trace_msg (fn () => "Failed to Skolemize " ^ Display.string_of_thm ctxt th);
wenzelm@32262
   555
        skolemize_nnf_list ctxt ths);
paulson@25694
   556
wenzelm@33339
   557
fun add_clauses th cls =
paulson@24937
   558
  let val ctxt0 = Variable.thm_context th
wenzelm@33339
   559
      val (cnfs, ctxt) = make_cnf [] th ctxt0
paulson@24937
   560
  in Variable.export ctxt ctxt0 cnfs @ cls end;
paulson@9840
   561
paulson@9840
   562
(*Make clauses from a list of theorems, previously Skolemized and put into nnf.
paulson@9840
   563
  The resulting clauses are HOL disjunctions.*)
blanchet@35869
   564
fun make_clauses_unsorted ths = fold_rev add_clauses ths [];
blanchet@35869
   565
val make_clauses = sort_clauses o make_clauses_unsorted;
quigley@15773
   566
paulson@16563
   567
(*Convert a list of clauses (disjunctions) to Horn clauses (contrapositives)*)
wenzelm@9869
   568
fun make_horns ths =
paulson@9840
   569
    name_thms "Horn#"
wenzelm@33339
   570
      (distinct Thm.eq_thm_prop (fold_rev (add_contras clause_rules) ths []));
paulson@9840
   571
paulson@9840
   572
(*Could simply use nprems_of, which would count remaining subgoals -- no
paulson@9840
   573
  discrimination as to their size!  With BEST_FIRST, fails for problem 41.*)
paulson@9840
   574
wenzelm@9869
   575
fun best_prolog_tac sizef horns =
paulson@9840
   576
    BEST_FIRST (has_fewer_prems 1, sizef) (prolog_step_tac horns 1);
paulson@9840
   577
wenzelm@9869
   578
fun depth_prolog_tac horns =
paulson@9840
   579
    DEPTH_FIRST (has_fewer_prems 1) (prolog_step_tac horns 1);
paulson@9840
   580
paulson@9840
   581
(*Return all negative clauses, as possible goal clauses*)
paulson@9840
   582
fun gocls cls = name_thms "Goal#" (map make_goal (neg_clauses cls));
paulson@9840
   583
wenzelm@32262
   584
fun skolemize_prems_tac ctxt prems =
wenzelm@32262
   585
    cut_facts_tac (skolemize_nnf_list ctxt prems) THEN'
paulson@9840
   586
    REPEAT o (etac exE);
paulson@9840
   587
paulson@22546
   588
(*Basis of all meson-tactics.  Supplies cltac with clauses: HOL disjunctions.
paulson@22546
   589
  Function mkcl converts theorems to clauses.*)
wenzelm@32262
   590
fun MESON mkcl cltac ctxt i st =
paulson@16588
   591
  SELECT_GOAL
wenzelm@35625
   592
    (EVERY [Object_Logic.atomize_prems_tac 1,
paulson@23552
   593
            rtac ccontr 1,
wenzelm@32283
   594
            Subgoal.FOCUS (fn {context = ctxt', prems = negs, ...} =>
wenzelm@32262
   595
                      EVERY1 [skolemize_prems_tac ctxt negs,
wenzelm@32283
   596
                              Subgoal.FOCUS (cltac o mkcl o #prems) ctxt']) ctxt 1]) i st
wenzelm@24300
   597
  handle THM _ => no_tac st;    (*probably from make_meta_clause, not first-order*)
paulson@9840
   598
paulson@9840
   599
(** Best-first search versions **)
paulson@9840
   600
paulson@16563
   601
(*ths is a list of additional clauses (HOL disjunctions) to use.*)
wenzelm@9869
   602
fun best_meson_tac sizef =
wenzelm@24300
   603
  MESON make_clauses
paulson@22546
   604
    (fn cls =>
paulson@9840
   605
         THEN_BEST_FIRST (resolve_tac (gocls cls) 1)
paulson@9840
   606
                         (has_fewer_prems 1, sizef)
paulson@9840
   607
                         (prolog_step_tac (make_horns cls) 1));
paulson@9840
   608
paulson@9840
   609
(*First, breaks the goal into independent units*)
wenzelm@32262
   610
fun safe_best_meson_tac ctxt =
wenzelm@32262
   611
     SELECT_GOAL (TRY (safe_tac (claset_of ctxt)) THEN
wenzelm@32262
   612
                  TRYALL (best_meson_tac size_of_subgoals ctxt));
paulson@9840
   613
paulson@9840
   614
(** Depth-first search version **)
paulson@9840
   615
paulson@9840
   616
val depth_meson_tac =
paulson@22546
   617
  MESON make_clauses
paulson@22546
   618
    (fn cls => EVERY [resolve_tac (gocls cls) 1, depth_prolog_tac (make_horns cls)]);
paulson@9840
   619
paulson@9840
   620
paulson@9840
   621
(** Iterative deepening version **)
paulson@9840
   622
paulson@9840
   623
(*This version does only one inference per call;
paulson@9840
   624
  having only one eq_assume_tac speeds it up!*)
wenzelm@9869
   625
fun prolog_step_tac' horns =
paulson@9840
   626
    let val (horn0s, hornps) = (*0 subgoals vs 1 or more*)
paulson@9840
   627
            take_prefix Thm.no_prems horns
paulson@9840
   628
        val nrtac = net_resolve_tac horns
paulson@9840
   629
    in  fn i => eq_assume_tac i ORELSE
paulson@9840
   630
                match_tac horn0s i ORELSE  (*no backtracking if unit MATCHES*)
paulson@9840
   631
                ((assume_tac i APPEND nrtac i) THEN check_tac)
paulson@9840
   632
    end;
paulson@9840
   633
wenzelm@9869
   634
fun iter_deepen_prolog_tac horns =
paulson@9840
   635
    ITER_DEEPEN (has_fewer_prems 1) (prolog_step_tac' horns);
paulson@9840
   636
wenzelm@32262
   637
fun iter_deepen_meson_tac ctxt ths = ctxt |> MESON make_clauses
wenzelm@32091
   638
  (fn cls =>
wenzelm@32091
   639
    (case (gocls (cls @ ths)) of
wenzelm@32091
   640
      [] => no_tac  (*no goal clauses*)
wenzelm@32091
   641
    | goes =>
wenzelm@32091
   642
        let
wenzelm@32091
   643
          val horns = make_horns (cls @ ths)
wenzelm@32955
   644
          val _ = trace_msg (fn () =>
wenzelm@32091
   645
            cat_lines ("meson method called:" ::
wenzelm@32262
   646
              map (Display.string_of_thm ctxt) (cls @ ths) @
wenzelm@32262
   647
              ["clauses:"] @ map (Display.string_of_thm ctxt) horns))
wenzelm@32091
   648
        in THEN_ITER_DEEPEN (resolve_tac goes 1) (has_fewer_prems 1) (prolog_step_tac' horns) end));
paulson@9840
   649
wenzelm@32262
   650
fun meson_tac ctxt ths =
wenzelm@32262
   651
  SELECT_GOAL (TRY (safe_tac (claset_of ctxt)) THEN TRYALL (iter_deepen_meson_tac ctxt ths));
wenzelm@9869
   652
wenzelm@9869
   653
paulson@14813
   654
(**** Code to support ordinary resolution, rather than Model Elimination ****)
paulson@14744
   655
wenzelm@24300
   656
(*Convert a list of clauses (disjunctions) to meta-level clauses (==>),
paulson@15008
   657
  with no contrapositives, for ordinary resolution.*)
paulson@14744
   658
paulson@14744
   659
(*Rules to convert the head literal into a negated assumption. If the head
paulson@14744
   660
  literal is already negated, then using notEfalse instead of notEfalse'
paulson@14744
   661
  prevents a double negation.*)
wenzelm@27239
   662
val notEfalse = read_instantiate @{context} [(("R", 0), "False")] notE;
paulson@14744
   663
val notEfalse' = rotate_prems 1 notEfalse;
paulson@14744
   664
wenzelm@24300
   665
fun negated_asm_of_head th =
paulson@14744
   666
    th RS notEfalse handle THM _ => th RS notEfalse';
paulson@14744
   667
paulson@26066
   668
(*Converting one theorem from a disjunction to a meta-level clause*)
paulson@26066
   669
fun make_meta_clause th =
wenzelm@33832
   670
  let val (fth,thaw) = Drule.legacy_freeze_thaw_robust th
paulson@26066
   671
  in  
paulson@26066
   672
      (zero_var_indexes o Thm.varifyT o thaw 0 o 
paulson@26066
   673
       negated_asm_of_head o make_horn resolution_clause_rules) fth
paulson@26066
   674
  end;
wenzelm@24300
   675
paulson@14744
   676
fun make_meta_clauses ths =
paulson@14744
   677
    name_thms "MClause#"
wenzelm@22360
   678
      (distinct Thm.eq_thm_prop (map make_meta_clause ths));
paulson@14744
   679
paulson@14744
   680
(*Permute a rule's premises to move the i-th premise to the last position.*)
paulson@14744
   681
fun make_last i th =
wenzelm@24300
   682
  let val n = nprems_of th
wenzelm@24300
   683
  in  if 1 <= i andalso i <= n
paulson@14744
   684
      then Thm.permute_prems (i-1) 1 th
paulson@15118
   685
      else raise THM("select_literal", i, [th])
paulson@14744
   686
  end;
paulson@14744
   687
paulson@14744
   688
(*Maps a rule that ends "... ==> P ==> False" to "... ==> ~P" while suppressing
paulson@14744
   689
  double-negations.*)
wenzelm@35410
   690
val negate_head = rewrite_rule [@{thm atomize_not}, not_not RS eq_reflection];
paulson@14744
   691
paulson@14744
   692
(*Maps the clause  [P1,...Pn]==>False to [P1,...,P(i-1),P(i+1),...Pn] ==> ~P*)
paulson@14744
   693
fun select_literal i cl = negate_head (make_last i cl);
paulson@14744
   694
paulson@18508
   695
paulson@14813
   696
(*Top-level Skolemization. Allows part of the conversion to clauses to be
wenzelm@24300
   697
  expressed as a tactic (or Isar method).  Each assumption of the selected
paulson@14813
   698
  goal is converted to NNF and then its existential quantifiers are pulled
wenzelm@24300
   699
  to the front. Finally, all existential quantifiers are eliminated,
paulson@14813
   700
  leaving !!-quantified variables. Perhaps Safe_tac should follow, but it
paulson@14813
   701
  might generate many subgoals.*)
mengj@18194
   702
wenzelm@32262
   703
fun skolemize_tac ctxt = SUBGOAL (fn (goal, i) =>
wenzelm@32262
   704
  let val ts = Logic.strip_assums_hyp goal
wenzelm@24300
   705
  in
wenzelm@32262
   706
    EVERY'
wenzelm@32262
   707
     [OldGoals.METAHYPS (fn hyps =>
wenzelm@32262
   708
        (cut_facts_tac (skolemize_nnf_list ctxt hyps) 1
wenzelm@32262
   709
          THEN REPEAT (etac exE 1))),
wenzelm@32262
   710
      REPEAT_DETERM_N (length ts) o (etac thin_rl)] i
wenzelm@32262
   711
  end);
mengj@18194
   712
paulson@9840
   713
end;