(*  Title:      HOL/Tools/res_axioms.ML

     Author:     Jia Meng, Cambridge University Computer Laboratory

 Transformation of axiom rules (elim/intro/etc) into CNF forms.

 *)

 signature RES_AXIOMS =

 sig

   val trace: bool Unsynchronized.ref

   val trace_msg: (unit -> string) -> unit

   val cnf_axiom: theory -> thm -> thm list

   val pairname: thm -> string * thm

   val multi_base_blacklist: string list

   val bad_for_atp: thm -> bool

   val type_has_topsort: typ -> bool

   val cnf_rules_pairs: theory -> (string * thm) list -> (thm * (string * int)) list

   val neg_clausify: thm list -> thm list

   val expand_defs_tac: thm -> tactic

   val combinators: thm -> thm

   val neg_conjecture_clauses: Proof.context -> thm -> int -> thm list * (string * typ) list

   val suppress_endtheory: bool Unsynchronized.ref

     (*for emergency use where endtheory causes problems*)

   val setup: theory -> theory

 end;

 structure Res_Axioms: RES_AXIOMS =

 struct

 val trace = Unsynchronized.ref false;

 fun trace_msg msg = if ! trace then tracing (msg ()) else ();

 fun freeze_thm th = #1 (Drule.legacy_freeze_thaw th);

 val type_has_topsort = Term.exists_subtype

   (fn TFree (_, []) => true

     | TVar (_, []) => true

     | _ => false);

 (**** Transformation of Elimination Rules into First-Order Formulas****)

 val cfalse = cterm_of @{theory HOL} HOLogic.false_const;

 val ctp_false = cterm_of @{theory HOL} (HOLogic.mk_Trueprop HOLogic.false_const);

 (*Converts an elim-rule into an equivalent theorem that does not have the

   predicate variable.  Leaves other theorems unchanged.  We simply instantiate the

   conclusion variable to False.*)

 fun transform_elim th =

   case concl_of th of    (*conclusion variable*)

        Const("Trueprop",_) $ (v as Var(_,Type("bool",[]))) =>

            Thm.instantiate ([], [(cterm_of @{theory HOL} v, cfalse)]) th

     | v as Var(_, Type("prop",[])) =>

            Thm.instantiate ([], [(cterm_of @{theory HOL} v, ctp_false)]) th

     | _ => th;

 (*To enforce single-threading*)

 exception Clausify_failure of theory;

 (**** SKOLEMIZATION BY INFERENCE (lcp) ****)

 fun rhs_extra_types lhsT rhs =

   let val lhs_vars = Term.add_tfreesT lhsT []

       fun add_new_TFrees (TFree v) =

             if member (op =) lhs_vars v then I else insert (op =) (TFree v)

         | add_new_TFrees _ = I

       val rhs_consts = fold_aterms (fn Const c => insert (op =) c | _ => I) rhs []

   in fold (#2 #> Term.fold_atyps add_new_TFrees) rhs_consts [] end;

 (*Traverse a theorem, declaring Skolem function definitions. String s is the suggested

   prefix for the Skolem constant.*)

 fun declare_skofuns s th =

   let

     val nref = Unsynchronized.ref 0    (* FIXME ??? *)

     fun dec_sko (Const ("Ex",_) $ (xtp as Abs (_, T, p))) (axs, thy) =

           (*Existential: declare a Skolem function, then insert into body and continue*)

           let

             val cname = "sko_" ^ s ^ "_" ^ Int.toString (Unsynchronized.inc nref)

             val args0 = OldTerm.term_frees xtp  (*get the formal parameter list*)

             val Ts = map type_of args0

             val extraTs = rhs_extra_types (Ts ---> T) xtp

             val argsx = map (fn T => Free (gensym "vsk", T)) extraTs

             val args = argsx @ args0

             val cT = extraTs ---> Ts ---> T

             val rhs = list_abs_free (map dest_Free args, HOLogic.choice_const T $ xtp)

                     (*Forms a lambda-abstraction over the formal parameters*)

             val (c, thy') =

               Sign.declare_const ((Binding.conceal (Binding.name cname), cT), NoSyn) thy

             val cdef = cname ^ "_def"

             val thy'' =

               Theory.add_defs_i true false [(Binding.name cdef, Logic.mk_equals (c, rhs))] thy'

             val ax = Thm.axiom thy'' (Sign.full_bname thy'' cdef)

           in dec_sko (subst_bound (list_comb (c, args), p)) (ax :: axs, thy'') end

       | dec_sko (Const ("All", _) $ (Abs (a, T, p))) thx =

           (*Universal quant: insert a free variable into body and continue*)

           let val fname = Name.variant (OldTerm.add_term_names (p, [])) a

           in dec_sko (subst_bound (Free (fname, T), p)) thx end

       | dec_sko (Const ("op &", _) $ p $ q) thx = dec_sko q (dec_sko p thx)

       | dec_sko (Const ("op |", _) $ p $ q) thx = dec_sko q (dec_sko p thx)

       | dec_sko (Const ("Trueprop", _) $ p) thx = dec_sko p thx

       | dec_sko t thx = thx (*Do nothing otherwise*)

   in fn thy => dec_sko (Thm.prop_of th) ([], thy) end;

 (*Traverse a theorem, accumulating Skolem function definitions.*)

 fun assume_skofuns s th =

   let val sko_count = Unsynchronized.ref 0   (* FIXME ??? *)

       fun dec_sko (Const ("Ex",_) $ (xtp as Abs(_,T,p))) defs =

             (*Existential: declare a Skolem function, then insert into body and continue*)

             let val skos = map (#1 o Logic.dest_equals) defs  (*existing sko fns*)

                 val args = subtract (op =) skos (OldTerm.term_frees xtp) (*the formal parameters*)

                 val Ts = map type_of args

                 val cT = Ts ---> T

                 val id = "sko_" ^ s ^ "_" ^ Int.toString (Unsynchronized.inc sko_count)

                 val c = Free (id, cT)

                 val rhs = list_abs_free (map dest_Free args,

                                          HOLogic.choice_const T $ xtp)

                       (*Forms a lambda-abstraction over the formal parameters*)

                 val def = Logic.mk_equals (c, rhs)

             in dec_sko (subst_bound (list_comb(c,args), p))

                        (def :: defs)

             end

         | dec_sko (Const ("All",_) $ Abs (a, T, p)) defs =

             (*Universal quant: insert a free variable into body and continue*)

             let val fname = Name.variant (OldTerm.add_term_names (p,[])) a

             in dec_sko (subst_bound (Free(fname,T), p)) defs end

         | dec_sko (Const ("op &", _) $ p $ q) defs = dec_sko q (dec_sko p defs)

         | dec_sko (Const ("op |", _) $ p $ q) defs = dec_sko q (dec_sko p defs)

         | dec_sko (Const ("Trueprop", _) $ p) defs = dec_sko p defs

         | dec_sko t defs = defs (*Do nothing otherwise*)

   in  dec_sko (prop_of th) []  end;

 (**** REPLACING ABSTRACTIONS BY COMBINATORS ****)

 (*Returns the vars of a theorem*)

 fun vars_of_thm th =

   map (Thm.cterm_of (theory_of_thm th) o Var) (Thm.fold_terms Term.add_vars th []);

 (*Make a version of fun_cong with a given variable name*)

 local

     val fun_cong' = fun_cong RS asm_rl; (*renumber f, g to prevent clashes with (a,0)*)

     val cx = hd (vars_of_thm fun_cong');

     val ty = typ_of (ctyp_of_term cx);

     val thy = theory_of_thm fun_cong;

     fun mkvar a = cterm_of thy (Var((a,0),ty));

 in

 fun xfun_cong x = Thm.instantiate ([], [(cx, mkvar x)]) fun_cong'

 end;

 (*Removes the lambdas from an equation of the form t = (%x. u).  A non-negative n,

   serves as an upper bound on how many to remove.*)

 fun strip_lambdas 0 th = th

   | strip_lambdas n th =

       case prop_of th of

           _ $ (Const ("op =", _) $ _ $ Abs (x,_,_)) =>

               strip_lambdas (n-1) (freeze_thm (th RS xfun_cong x))

         | _ => th;

 val lambda_free = not o Term.has_abs;

 val [f_B,g_B] = map (cterm_of @{theory}) (OldTerm.term_vars (prop_of @{thm abs_B}));

 val [g_C,f_C] = map (cterm_of @{theory}) (OldTerm.term_vars (prop_of @{thm abs_C}));

 val [f_S,g_S] = map (cterm_of @{theory}) (OldTerm.term_vars (prop_of @{thm abs_S}));

 (*FIXME: requires more use of cterm constructors*)

 fun abstract ct =

   let

       val thy = theory_of_cterm ct

       val Abs(x,_,body) = term_of ct

       val Type("fun",[xT,bodyT]) = typ_of (ctyp_of_term ct)

       val cxT = ctyp_of thy xT and cbodyT = ctyp_of thy bodyT

       fun makeK() = instantiate' [SOME cxT, SOME cbodyT] [SOME (cterm_of thy body)] @{thm abs_K}

   in

       case body of

           Const _ => makeK()

         | Free _ => makeK()

         | Var _ => makeK()  (*though Var isn't expected*)

         | Bound 0 => instantiate' [SOME cxT] [] @{thm abs_I} (*identity: I*)

         | rator$rand =>

             if loose_bvar1 (rator,0) then (*C or S*)

                if loose_bvar1 (rand,0) then (*S*)

                  let val crator = cterm_of thy (Abs(x,xT,rator))

                      val crand = cterm_of thy (Abs(x,xT,rand))

                      val abs_S' = cterm_instantiate [(f_S,crator),(g_S,crand)] @{thm abs_S}

                      val (_,rhs) = Thm.dest_equals (cprop_of abs_S')

                  in

                    Thm.transitive abs_S' (Conv.binop_conv abstract rhs)

                  end

                else (*C*)

                  let val crator = cterm_of thy (Abs(x,xT,rator))

                      val abs_C' = cterm_instantiate [(f_C,crator),(g_C,cterm_of thy rand)] @{thm abs_C}

                      val (_,rhs) = Thm.dest_equals (cprop_of abs_C')

                  in

                    Thm.transitive abs_C' (Conv.fun_conv (Conv.arg_conv abstract) rhs)

                  end

             else if loose_bvar1 (rand,0) then (*B or eta*)

                if rand = Bound 0 then eta_conversion ct

                else (*B*)

                  let val crand = cterm_of thy (Abs(x,xT,rand))

                      val crator = cterm_of thy rator

                      val abs_B' = cterm_instantiate [(f_B,crator),(g_B,crand)] @{thm abs_B}

                      val (_,rhs) = Thm.dest_equals (cprop_of abs_B')

                  in

                    Thm.transitive abs_B' (Conv.arg_conv abstract rhs)

                  end

             else makeK()

         | _ => error "abstract: Bad term"

   end;

 (*Traverse a theorem, declaring abstraction function definitions. String s is the suggested

   prefix for the constants.*)

 fun combinators_aux ct =

   if lambda_free (term_of ct) then reflexive ct

   else

   case term_of ct of

       Abs _ =>

         let val (cv, cta) = Thm.dest_abs NONE ct

             val (v, _) = dest_Free (term_of cv)

             val u_th = combinators_aux cta

             val cu = Thm.rhs_of u_th

             val comb_eq = abstract (Thm.cabs cv cu)

         in transitive (abstract_rule v cv u_th) comb_eq end

     | _ $ _ =>

         let val (ct1, ct2) = Thm.dest_comb ct

         in  combination (combinators_aux ct1) (combinators_aux ct2)  end;

 fun combinators th =

   if lambda_free (prop_of th) then th

   else

     let val th = Drule.eta_contraction_rule th

         val eqth = combinators_aux (cprop_of th)

     in  equal_elim eqth th   end

     handle THM (msg,_,_) =>

       (warning (cat_lines

         ["Error in the combinator translation of " ^ Display.string_of_thm_without_context th,

           "  Exception message: " ^ msg]);

        TrueI);  (*A type variable of sort {} will cause make abstraction fail.*)

 (*cterms are used throughout for efficiency*)

 val cTrueprop = Thm.cterm_of @{theory HOL} HOLogic.Trueprop;

 (*cterm version of mk_cTrueprop*)

 fun c_mkTrueprop A = Thm.capply cTrueprop A;

 (*Given an abstraction over n variables, replace the bound variables by free

   ones. Return the body, along with the list of free variables.*)

 fun c_variant_abs_multi (ct0, vars) =

       let val (cv,ct) = Thm.dest_abs NONE ct0

       in  c_variant_abs_multi (ct, cv::vars)  end

       handle CTERM _ => (ct0, rev vars);

 (*Given the definition of a Skolem function, return a theorem to replace

   an existential formula by a use of that function.

    Example: "EX x. x : A & x ~: B ==> sko A B : A & sko A B ~: B"  [.] *)

 fun skolem_of_def def =

   let val (c,rhs) = Thm.dest_equals (cprop_of (freeze_thm def))

       val (ch, frees) = c_variant_abs_multi (rhs, [])

       val (chilbert,cabs) = Thm.dest_comb ch

       val thy = Thm.theory_of_cterm chilbert

       val t = Thm.term_of chilbert

       val T = case t of Const ("Hilbert_Choice.Eps", Type("fun",[_,T])) => T

                       | _ => raise THM ("skolem_of_def: expected Eps", 0, [def])

       val cex = Thm.cterm_of thy (HOLogic.exists_const T)

       val ex_tm = c_mkTrueprop (Thm.capply cex cabs)

       and conc =  c_mkTrueprop (Drule.beta_conv cabs (Drule.list_comb(c,frees)));

       fun tacf [prem] = rewrite_goals_tac [def] THEN rtac (prem RS @{thm someI_ex}) 1

   in  Goal.prove_internal [ex_tm] conc tacf

        |> forall_intr_list frees

        |> Thm.forall_elim_vars 0  (*Introduce Vars, but don't discharge defs.*)

        |> Thm.varifyT

   end;

 (*Converts an Isabelle theorem (intro, elim or simp format, even higher-order) into NNF.*)

 fun to_nnf th ctxt0 =

   let val th1 = th |> transform_elim |> zero_var_indexes

       val ((_, [th2]), ctxt) = Variable.import true [th1] ctxt0

       val th3 = th2

         |> Conv.fconv_rule Object_Logic.atomize

         |> Meson.make_nnf ctxt |> strip_lambdas ~1

   in  (th3, ctxt)  end;

 (*Generate Skolem functions for a theorem supplied in nnf*)

 fun assume_skolem_of_def s th =

   map (skolem_of_def o assume o (cterm_of (theory_of_thm th))) (assume_skofuns s th);

 (*** Blacklisting (duplicated in Res_ATP?) ***)

 val max_lambda_nesting = 3;

 fun excessive_lambdas (f$t, k) = excessive_lambdas (f,k) orelse excessive_lambdas (t,k)

   | excessive_lambdas (Abs(_,_,t), k) = k=0 orelse excessive_lambdas (t,k-1)

   | excessive_lambdas _ = false;

 fun is_formula_type T = (T = HOLogic.boolT orelse T = propT);

 (*Don't count nested lambdas at the level of formulas, as they are quantifiers*)

 fun excessive_lambdas_fm Ts (Abs(_,T,t)) = excessive_lambdas_fm (T::Ts) t

   | excessive_lambdas_fm Ts t =

       if is_formula_type (fastype_of1 (Ts, t))

       then exists (excessive_lambdas_fm Ts) (#2 (strip_comb t))

       else excessive_lambdas (t, max_lambda_nesting);

 (*The max apply_depth of any metis call in Metis_Examples (on 31-10-2007) was 11.*)

 val max_apply_depth = 15;

 fun apply_depth (f$t) = Int.max (apply_depth f, apply_depth t + 1)

   | apply_depth (Abs(_,_,t)) = apply_depth t

   | apply_depth _ = 0;

 fun too_complex t =

   apply_depth t > max_apply_depth orelse

   Meson.too_many_clauses NONE t orelse

   excessive_lambdas_fm [] t;

 fun is_strange_thm th =

   case head_of (concl_of th) of

       Const (a, _) => (a <> "Trueprop" andalso a <> "==")

     | _ => false;

 fun bad_for_atp th =

   too_complex (prop_of th)

   orelse exists_type type_has_topsort (prop_of th)

   orelse is_strange_thm th;

 val multi_base_blacklist =

   ["defs","select_defs","update_defs","induct","inducts","split","splits","split_asm",

    "cases","ext_cases"];  (* FIXME put other record thms here, or declare as "noatp" *)

 (*Keep the full complexity of the original name*)

 fun flatten_name s = space_implode "_X" (Long_Name.explode s);

 fun fake_name th =

   if Thm.has_name_hint th then flatten_name (Thm.get_name_hint th)

   else gensym "unknown_thm_";

 (*Skolemize a named theorem, with Skolem functions as additional premises.*)

 fun skolem_thm (s, th) =

   if member (op =) multi_base_blacklist (Long_Name.base_name s) orelse bad_for_atp th then []

   else

     let

       val ctxt0 = Variable.thm_context th

       val (nnfth, ctxt1) = to_nnf th ctxt0

       val (cnfs, ctxt2) = Meson.make_cnf (assume_skolem_of_def s nnfth) nnfth ctxt1

     in  cnfs |> map combinators |> Variable.export ctxt2 ctxt0 |> Meson.finish_cnf  end

     handle THM _ => [];

 (*The cache prevents repeated clausification of a theorem, and also repeated declaration of

   Skolem functions.*)

 structure ThmCache = Theory_Data

 (

   type T = thm list Thmtab.table * unit Symtab.table;

   val empty = (Thmtab.empty, Symtab.empty);

   val extend = I;

   fun merge ((cache1, seen1), (cache2, seen2)) : T =

     (Thmtab.merge (K true) (cache1, cache2), Symtab.merge (K true) (seen1, seen2));

 );

 val lookup_cache = Thmtab.lookup o #1 o ThmCache.get;

 val already_seen = Symtab.defined o #2 o ThmCache.get;

 val update_cache = ThmCache.map o apfst o Thmtab.update;

 fun mark_seen name = ThmCache.map (apsnd (Symtab.update (name, ())));

 (*Exported function to convert Isabelle theorems into axiom clauses*)

 fun cnf_axiom thy th0 =

   let val th = Thm.transfer thy th0 in

     case lookup_cache thy th of

       NONE => map Thm.close_derivation (skolem_thm (fake_name th, th))

     | SOME cls => cls

   end;

 (**** Rules from the context ****)

 fun pairname th = (Thm.get_name_hint th, th);

 (**** Translate a set of theorems into CNF ****)

 fun pair_name_cls k (n, []) = []

   | pair_name_cls k (n, cls::clss) = (cls, (n,k)) :: pair_name_cls (k+1) (n, clss)

 fun cnf_rules_pairs_aux _ pairs [] = pairs

   | cnf_rules_pairs_aux thy pairs ((name,th)::ths) =

       let val pairs' = (pair_name_cls 0 (name, cnf_axiom thy th)) @ pairs

                        handle THM _ => pairs | Res_Clause.CLAUSE _ => pairs

       in  cnf_rules_pairs_aux thy pairs' ths  end;

 (*The combination of rev and tail recursion preserves the original order*)

 fun cnf_rules_pairs thy l = cnf_rules_pairs_aux thy [] (rev l);

 (**** Convert all facts of the theory into clauses (Res_Clause.clause, or Res_HOL_Clause.clause) ****)

 local

 fun skolem_def (name, th) thy =

   let val ctxt0 = Variable.thm_context th in

     (case try (to_nnf th) ctxt0 of

       NONE => (NONE, thy)

     | SOME (nnfth, ctxt1) =>

         let val (defs, thy') = declare_skofuns (flatten_name name) nnfth thy

         in (SOME (th, ctxt0, ctxt1, nnfth, defs), thy') end)

   end;

 fun skolem_cnfs (th, ctxt0, ctxt1, nnfth, defs) =

   let

     val (cnfs, ctxt2) = Meson.make_cnf (map skolem_of_def defs) nnfth ctxt1;

     val cnfs' = cnfs

       |> map combinators

       |> Variable.export ctxt2 ctxt0

       |> Meson.finish_cnf

       |> map Thm.close_derivation;

     in (th, cnfs') end;

 in

 fun saturate_skolem_cache thy =

   let

     val facts = PureThy.facts_of thy;

     val new_facts = (facts, []) |-> Facts.fold_static (fn (name, ths) =>

       if Facts.is_concealed facts name orelse already_seen thy name then I

       else cons (name, ths));

     val new_thms = (new_facts, []) |-> fold (fn (name, ths) =>

       if member (op =) multi_base_blacklist (Long_Name.base_name name) then I

       else fold_index (fn (i, th) =>

         if bad_for_atp th orelse is_some (lookup_cache thy th) then I

         else cons (name ^ "_" ^ string_of_int (i + 1), Thm.transfer thy th)) ths);

   in

     if null new_facts then NONE

     else

       let

         val (defs, thy') = thy

           |> fold (mark_seen o #1) new_facts

           |> fold_map skolem_def (sort_distinct (Thm.thm_ord o pairself snd) new_thms)

           |>> map_filter I;

         val cache_entries = Par_List.map skolem_cnfs defs;

       in SOME (fold update_cache cache_entries thy') end

   end;

 end;

 val suppress_endtheory = Unsynchronized.ref false;

 fun clause_cache_endtheory thy =

   if ! suppress_endtheory then NONE

   else saturate_skolem_cache thy;

 (*The cache can be kept smaller by inspecting the prop of each thm. Can ignore all that are

   lambda_free, but then the individual theory caches become much bigger.*)

 (*** meson proof methods ***)

 (*Expand all new definitions of abstraction or Skolem functions in a proof state.*)

 fun is_absko (Const ("==", _) $ Free (a,_) $ u) = String.isPrefix "sko_" a

   | is_absko _ = false;

 fun is_okdef xs (Const ("==", _) $ t $ u) =   (*Definition of Free, not in certain terms*)

       is_Free t andalso not (member (op aconv) xs t)

   | is_okdef _ _ = false

 (*This function tries to cope with open locales, which introduce hypotheses of the form

   Free == t, conjecture clauses, which introduce various hypotheses, and also definitions

   of sko_ functions. *)

 fun expand_defs_tac st0 st =

   let val hyps0 = #hyps (rep_thm st0)

       val hyps = #hyps (crep_thm st)

       val newhyps = filter_out (member (op aconv) hyps0 o Thm.term_of) hyps

       val defs = filter (is_absko o Thm.term_of) newhyps

       val remaining_hyps = filter_out (member (op aconv) (map Thm.term_of defs))

                                       (map Thm.term_of hyps)

       val fixed = OldTerm.term_frees (concl_of st) @

                   fold (union (op aconv)) (map OldTerm.term_frees remaining_hyps) []

   in Seq.of_list [Local_Defs.expand (filter (is_okdef fixed o Thm.term_of) defs) st] end;

 fun meson_general_tac ctxt ths i st0 =

   let

     val thy = ProofContext.theory_of ctxt

     val ctxt0 = Classical.put_claset HOL_cs ctxt

   in (Meson.meson_tac ctxt0 (maps (cnf_axiom thy) ths) i THEN expand_defs_tac st0) st0 end;

 val meson_method_setup =

   Method.setup @{binding meson} (Attrib.thms >> (fn ths => fn ctxt =>

     SIMPLE_METHOD' (CHANGED_PROP o meson_general_tac ctxt ths)))

     "MESON resolution proof procedure";

 (*** Converting a subgoal into negated conjecture clauses. ***)

 fun neg_skolemize_tac ctxt =

   EVERY' [rtac ccontr, Object_Logic.atomize_prems_tac, Meson.skolemize_tac ctxt];

 val neg_clausify = Meson.make_clauses #> map combinators #> Meson.finish_cnf;

 fun neg_conjecture_clauses ctxt st0 n =

   let

     val st = Seq.hd (neg_skolemize_tac ctxt n st0)

     val ({params, prems, ...}, _) = Subgoal.focus (Variable.set_body false ctxt) n st

   in (neg_clausify prems, map (Term.dest_Free o Thm.term_of o #2) params) end;

 (*Conversion of a subgoal to conjecture clauses. Each clause has

   leading !!-bound universal variables, to express generality. *)

 fun neg_clausify_tac ctxt =

   neg_skolemize_tac ctxt THEN'

   SUBGOAL (fn (prop, i) =>

     let val ts = Logic.strip_assums_hyp prop in

       EVERY'

        [Subgoal.FOCUS

          (fn {prems, ...} =>

            (Method.insert_tac

              (map forall_intr_vars (neg_clausify prems)) i)) ctxt,

         REPEAT_DETERM_N (length ts) o etac thin_rl] i

      end);

 val neg_clausify_setup =

   Method.setup @{binding neg_clausify} (Scan.succeed (SIMPLE_METHOD' o neg_clausify_tac))

   "conversion of goal to conjecture clauses";

 (** Attribute for converting a theorem into clauses **)

 val clausify_setup =

   Attrib.setup @{binding clausify}

     (Scan.lift OuterParse.nat >>

       (fn i => Thm.rule_attribute (fn context => fn th =>

           Meson.make_meta_clause (nth (cnf_axiom (Context.theory_of context) th) i))))

   "conversion of theorem to clauses";

 (** setup **)

 val setup =

   meson_method_setup #>

   neg_clausify_setup #>

   clausify_setup #>

   perhaps saturate_skolem_cache #>

   Theory.at_end clause_cache_endtheory;

 end;