src/Pure/thm.ML

Non-matching congruence rule in rewriter is simply ignored.
Used to cause error message.

(*  Title:      Pure/thm.ML
    ID:         $Id$
    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
    Copyright   1994  University of Cambridge

The core of Isabelle's Meta Logic: certified types and terms, meta
theorems, meta rules (including resolution and simplification).
*)

signature THM =
  sig
  (*certified types*)
  type ctyp
  val rep_ctyp          : ctyp -> {sign: Sign.sg, T: typ}
  val typ_of            : ctyp -> typ
  val ctyp_of           : Sign.sg -> typ -> ctyp
  val read_ctyp         : Sign.sg -> string -> ctyp

  (*certified terms*)
  type cterm
  exception CTERM of string
  val rep_cterm         : cterm -> {sign: Sign.sg, t: term, T: typ,
                                    maxidx: int}
  val term_of           : cterm -> term
  val cterm_of          : Sign.sg -> term -> cterm
  val read_cterm        : Sign.sg -> string * typ -> cterm
  val read_cterms       : Sign.sg -> string list * typ list -> cterm list
  val cterm_fun         : (term -> term) -> (cterm -> cterm)
  val dest_cimplies     : cterm -> cterm * cterm
  val dest_comb         : cterm -> cterm * cterm
  val dest_abs          : cterm -> cterm * cterm
  val capply            : cterm -> cterm -> cterm
  val cabs              : cterm -> cterm -> cterm
  val read_def_cterm    :
    Sign.sg * (indexname -> typ option) * (indexname -> sort option) ->
    string list -> bool -> string * typ -> cterm * (indexname * typ) list

  (*theories*)

  (*proof terms [must duplicate declaration as a specification]*)
  val full_deriv	: bool ref
  datatype rule = 
      MinProof				
    | Axiom		of theory * string
    | Theorem		of theory * string	
    | Assume		of cterm
    | Implies_intr	of cterm
    | Implies_intr_shyps
    | Implies_intr_hyps
    | Implies_elim 
    | Forall_intr	of cterm
    | Forall_elim	of cterm
    | Reflexive		of cterm
    | Symmetric 
    | Transitive
    | Beta_conversion	of cterm
    | Extensional
    | Abstract_rule	of string * cterm
    | Combination
    | Equal_intr
    | Equal_elim
    | Trivial		of cterm
    | Lift_rule		of cterm * int 
    | Assumption	of int * Envir.env option
    | Instantiate	of (indexname * ctyp) list * (cterm * cterm) list
    | Bicompose		of bool * bool * int * int * Envir.env
    | Flexflex_rule	of Envir.env		
    | Class_triv	of theory * class	
    | VarifyT
    | FreezeT
    | RewriteC		of cterm
    | CongC		of cterm
    | Rewrite_cterm	of cterm
    | Rename_params_rule of string list * int;

  datatype deriv = Infer  of rule * deriv list
		 | Oracle of theory * Sign.sg * exn;

  (*meta theorems*)
  type thm
  exception THM of string * int * thm list
  val rep_thm           : thm -> {sign: Sign.sg, der: deriv, maxidx: int,
				  shyps: sort list, hyps: term list, 
				  prop: term}
  val crep_thm          : thm -> {sign: Sign.sg, der: deriv, maxidx: int,
				  shyps: sort list, hyps: cterm list, 
				  prop: cterm}
  val stamps_of_thm     : thm -> string ref list
  val tpairs_of         : thm -> (term * term) list
  val prems_of          : thm -> term list
  val nprems_of         : thm -> int
  val concl_of          : thm -> term
  val cprop_of          : thm -> cterm
  val extra_shyps       : thm -> sort list
  val force_strip_shyps : bool ref      (* FIXME tmp *)
  val strip_shyps       : thm -> thm
  val implies_intr_shyps: thm -> thm
  val get_axiom         : theory -> string -> thm
  val name_thm          : theory * string * thm -> thm
  val axioms_of         : theory -> (string * thm) list

  (*meta rules*)
  val assume            : cterm -> thm
  val compress          : thm -> thm
  val implies_intr      : cterm -> thm -> thm
  val implies_elim      : thm -> thm -> thm
  val forall_intr       : cterm -> thm -> thm
  val forall_elim       : cterm -> thm -> thm
  val flexpair_def      : thm
  val reflexive         : cterm -> thm
  val symmetric         : thm -> thm
  val transitive        : thm -> thm -> thm
  val beta_conversion   : cterm -> thm
  val extensional       : thm -> thm
  val abstract_rule     : string -> cterm -> thm -> thm
  val combination       : thm -> thm -> thm
  val equal_intr        : thm -> thm -> thm
  val equal_elim        : thm -> thm -> thm
  val implies_intr_hyps : thm -> thm
  val flexflex_rule     : thm -> thm Sequence.seq
  val instantiate       :
    (indexname * ctyp) list * (cterm * cterm) list -> thm -> thm
  val trivial           : cterm -> thm
  val class_triv        : theory -> class -> thm
  val varifyT           : thm -> thm
  val freezeT           : thm -> thm
  val dest_state        : thm * int ->
    (term * term) list * term list * term * term
  val lift_rule         : (thm * int) -> thm -> thm
  val assumption        : int -> thm -> thm Sequence.seq
  val eq_assumption     : int -> thm -> thm
  val rename_params_rule: string list * int -> thm -> thm
  val bicompose         : bool -> bool * thm * int ->
    int -> thm -> thm Sequence.seq
  val biresolution      : bool -> (bool * thm) list ->
    int -> thm -> thm Sequence.seq

  (*meta simplification*)
  type meta_simpset
  exception SIMPLIFIER of string * thm
  val empty_mss         : meta_simpset
  val add_simps         : meta_simpset * thm list -> meta_simpset
  val del_simps         : meta_simpset * thm list -> meta_simpset
  val mss_of            : thm list -> meta_simpset
  val add_congs         : meta_simpset * thm list -> meta_simpset
  val add_prems         : meta_simpset * thm list -> meta_simpset
  val prems_of_mss      : meta_simpset -> thm list
  val set_mk_rews       : meta_simpset * (thm -> thm list) -> meta_simpset
  val mk_rews_of_mss    : meta_simpset -> thm -> thm list
  val trace_simp        : bool ref
  val rewrite_cterm     : bool * bool -> meta_simpset ->
                          (meta_simpset -> thm -> thm option) -> cterm -> thm

  val invoke_oracle	: theory * Sign.sg * exn -> thm
end;

structure Thm : THM =
struct

(*** Certified terms and types ***)

(** certified types **)

(*certified typs under a signature*)

datatype ctyp = Ctyp of {sign: Sign.sg, T: typ};

fun rep_ctyp (Ctyp args) = args;
fun typ_of (Ctyp {T, ...}) = T;

fun ctyp_of sign T =
  Ctyp {sign = sign, T = Sign.certify_typ sign T};

fun read_ctyp sign s =
  Ctyp {sign = sign, T = Sign.read_typ (sign, K None) s};



(** certified terms **)

(*certified terms under a signature, with checked typ and maxidx of Vars*)

datatype cterm = Cterm of {sign: Sign.sg, t: term, T: typ, maxidx: int};

fun rep_cterm (Cterm args) = args;
fun term_of (Cterm {t, ...}) = t;

(*create a cterm by checking a "raw" term with respect to a signature*)
fun cterm_of sign tm =
  let val (t, T, maxidx) = Sign.certify_term sign tm
  in  Cterm {sign = sign, t = t, T = T, maxidx = maxidx}
  end;

fun cterm_fun f (Cterm {sign, t, ...}) = cterm_of sign (f t);


(*dest_implies for cterms. Note T=prop below*)
fun dest_cimplies (Cterm{sign, T, maxidx, t=Const("==>", _) $ A $ B}) =
       (Cterm{sign=sign, T=T, maxidx=maxidx, t=A},
        Cterm{sign=sign, T=T, maxidx=maxidx, t=B})
  | dest_cimplies ct = raise TERM ("dest_cimplies", [term_of ct]);

exception CTERM of string;

(*Destruct application in cterms*)
fun dest_comb (Cterm{sign, T, maxidx, t = A $ B}) =
      let val typeA = fastype_of A;
          val typeB =
            case typeA of Type("fun",[S,T]) => S
                        | _ => error "Function type expected in dest_comb";
      in
      (Cterm {sign=sign, maxidx=maxidx, t=A, T=typeA},
       Cterm {sign=sign, maxidx=maxidx, t=B, T=typeB})
      end
  | dest_comb _ = raise CTERM "dest_comb";

(*Destruct abstraction in cterms*)
fun dest_abs (Cterm {sign, T as Type("fun",[_,S]), maxidx, t=Abs(x,ty,M)}) = 
      let val (y,N) = variant_abs (x,ty,M)
      in (Cterm {sign = sign, T = ty, maxidx = 0, t = Free(y,ty)},
          Cterm {sign = sign, T = S, maxidx = maxidx, t = N})
      end
  | dest_abs _ = raise CTERM "dest_abs";

(*Form cterm out of a function and an argument*)
fun capply (Cterm {t=f, sign=sign1, T=Type("fun",[dty,rty]), maxidx=maxidx1})
           (Cterm {t=x, sign=sign2, T, maxidx=maxidx2}) =
      if T = dty then Cterm{t=f$x, sign=Sign.merge(sign1,sign2), T=rty,
                            maxidx=max[maxidx1, maxidx2]}
      else raise CTERM "capply: types don't agree"
  | capply _ _ = raise CTERM "capply: first arg is not a function"

fun cabs (Cterm {t=Free(a,ty), sign=sign1, T=T1, maxidx=maxidx1})
         (Cterm {t=t2, sign=sign2, T=T2, maxidx=maxidx2}) =
      Cterm {t=absfree(a,ty,t2), sign=Sign.merge(sign1,sign2),
             T = ty --> T2, maxidx=max[maxidx1, maxidx2]}
  | cabs _ _ = raise CTERM "cabs: first arg is not a free variable";

(** read cterms **)   (*exception ERROR*)

(*read term, infer types, certify term*)
fun read_def_cterm (sign, types, sorts) used freeze (a, T) =
  let
    val T' = Sign.certify_typ sign T
      handle TYPE (msg, _, _) => error msg;
    val ts = Syntax.read (#syn (Sign.rep_sg sign)) T' a;
    val (_, t', tye) =
          Sign.infer_types sign types sorts used freeze (ts, T');
    val ct = cterm_of sign t'
      handle TYPE arg => error (Sign.exn_type_msg sign arg)
	   | TERM (msg, _) => error msg;
  in (ct, tye) end;

fun read_cterm sign = #1 o read_def_cterm (sign, K None, K None) [] true;

(*read a list of terms, matching them against a list of expected types.
  NO disambiguation of alternative parses via type-checking -- it is just
  not practical.*)
fun read_cterms sign (bs, Ts) =
  let
    val {tsig, syn, ...} = Sign.rep_sg sign
    fun read (b,T) =
	case Syntax.read syn T b of
	    [t] => t
	  | _   => error("Error or ambiguity in parsing of " ^ b)
    val (us,_) = Type.infer_types(tsig, Sign.const_type sign, 
				  K None, K None, 
				  [], true, 
				  map (Sign.certify_typ sign) Ts, 
				  map read (bs~~Ts))
  in  map (cterm_of sign) us  end
  handle TYPE arg => error (Sign.exn_type_msg sign arg)
       | TERM (msg, _) => error msg;



(*** Derivations ***)

(*Names of rules in derivations.  Includes logically trivial rules, if 
  executed in ML.*)
datatype rule = 
    MinProof				(*for building minimal proof terms*)
(*Axioms/theorems*)
  | Axiom		of theory * string
  | Theorem		of theory * string	(*via theorem db*)
(*primitive inferences and compound versions of them*)
  | Assume		of cterm
  | Implies_intr	of cterm
  | Implies_intr_shyps
  | Implies_intr_hyps
  | Implies_elim 
  | Forall_intr		of cterm
  | Forall_elim		of cterm
  | Reflexive		of cterm
  | Symmetric 
  | Transitive
  | Beta_conversion	of cterm
  | Extensional
  | Abstract_rule	of string * cterm
  | Combination
  | Equal_intr
  | Equal_elim
(*derived rules for tactical proof*)
  | Trivial		of cterm
	(*For lift_rule, the proof state is not a premise.
	  Use cterm instead of thm to avoid mutual recursion.*)
  | Lift_rule		of cterm * int 
  | Assumption		of int * Envir.env option (*includes eq_assumption*)
  | Instantiate		of (indexname * ctyp) list * (cterm * cterm) list
  | Bicompose		of bool * bool * int * int * Envir.env
  | Flexflex_rule	of Envir.env		(*identifies unifier chosen*)
(*other derived rules*)
  | Class_triv		of theory * class	(*derived rule????*)
  | VarifyT
  | FreezeT
(*for the simplifier*)
  | RewriteC		of cterm
  | CongC		of cterm
  | Rewrite_cterm	of cterm
(*Logical identities, recorded since they are part of the proof process*)
  | Rename_params_rule	of string list * int;


datatype deriv = Infer	of rule * deriv list
	       | Oracle	of theory * Sign.sg * exn;


val full_deriv = ref false;


(*Suppress all atomic inferences, if using minimal derivations*)
fun squash_derivs (Infer (_, []) :: drvs) =        squash_derivs drvs
  | squash_derivs (der :: ders)           = der :: squash_derivs ders
  | squash_derivs []                      = [];

(*Ensure sharing of the most likely derivation, the empty one!*)
val min_infer = Infer (MinProof, []);

(*Make a minimal inference*)
fun make_min_infer []    = min_infer
  | make_min_infer [der] = der
  | make_min_infer ders  = Infer (MinProof, ders);

fun infer_derivs (rl, [])   = Infer (rl, [])
  | infer_derivs (rl, ders) =
    if !full_deriv then Infer (rl, ders)
    else make_min_infer (squash_derivs ders);


(*** Meta theorems ***)

datatype thm = Thm of
  {sign: Sign.sg,		(*signature for hyps and prop*)
   der: deriv,			(*derivation*)
   maxidx: int,			(*maximum index of any Var or TVar*)
   shyps: sort list,		(* FIXME comment *)
   hyps: term list,		(*hypotheses*)
   prop: term};			(*conclusion*)

fun rep_thm (Thm args) = args;

(*Version of rep_thm returning cterms instead of terms*)
fun crep_thm (Thm {sign, der, maxidx, shyps, hyps, prop}) =
  let fun ctermf max t = Cterm{sign=sign, t=t, T=propT, maxidx=max};
  in {sign=sign, der=der, maxidx=maxidx, shyps=shyps,
      hyps = map (ctermf ~1) hyps,
      prop = ctermf maxidx prop}
  end;

(*errors involving theorems*)
exception THM of string * int * thm list;


val sign_of_thm = #sign o rep_thm;
val stamps_of_thm = #stamps o Sign.rep_sg o sign_of_thm;

(*merge signatures of two theorems; raise exception if incompatible*)
fun merge_thm_sgs (th1, th2) =
  Sign.merge (pairself sign_of_thm (th1, th2))
    handle TERM (msg, _) => raise THM (msg, 0, [th1, th2]);


(*maps object-rule to tpairs*)
fun tpairs_of (Thm {prop, ...}) = #1 (Logic.strip_flexpairs prop);

(*maps object-rule to premises*)
fun prems_of (Thm {prop, ...}) =
  Logic.strip_imp_prems (Logic.skip_flexpairs prop);

(*counts premises in a rule*)
fun nprems_of (Thm {prop, ...}) =
  Logic.count_prems (Logic.skip_flexpairs prop, 0);

(*maps object-rule to conclusion*)
fun concl_of (Thm {prop, ...}) = Logic.strip_imp_concl prop;

(*the statement of any thm is a cterm*)
fun cprop_of (Thm {sign, maxidx, prop, ...}) =
  Cterm {sign = sign, maxidx = maxidx, T = propT, t = prop};



(** sort contexts of theorems **)

(* basic utils *)

(*accumulate sorts suppressing duplicates; these are coded low level
  to improve efficiency a bit*)

fun add_typ_sorts (Type (_, Ts), Ss) = add_typs_sorts (Ts, Ss)
  | add_typ_sorts (TFree (_, S), Ss) = S ins Ss
  | add_typ_sorts (TVar (_, S), Ss) = S ins Ss
and add_typs_sorts ([], Ss) = Ss
  | add_typs_sorts (T :: Ts, Ss) = add_typs_sorts (Ts, add_typ_sorts (T, Ss));

fun add_term_sorts (Const (_, T), Ss) = add_typ_sorts (T, Ss)
  | add_term_sorts (Free (_, T), Ss) = add_typ_sorts (T, Ss)
  | add_term_sorts (Var (_, T), Ss) = add_typ_sorts (T, Ss)
  | add_term_sorts (Bound _, Ss) = Ss
  | add_term_sorts (Abs (_, T, t), Ss) = add_term_sorts (t, add_typ_sorts (T, Ss))
  | add_term_sorts (t $ u, Ss) = add_term_sorts (t, add_term_sorts (u, Ss));

fun add_terms_sorts ([], Ss) = Ss
  | add_terms_sorts (t :: ts, Ss) = add_terms_sorts (ts, add_term_sorts (t, Ss));

fun env_codT (Envir.Envir {iTs, ...}) = map snd iTs;

fun add_env_sorts (env, Ss) =
  add_terms_sorts (map snd (Envir.alist_of env),
    add_typs_sorts (env_codT env, Ss));

fun add_thm_sorts (Thm {hyps, prop, ...}, Ss) =
  add_terms_sorts (hyps, add_term_sorts (prop, Ss));

fun add_thms_shyps ([], Ss) = Ss
  | add_thms_shyps (Thm {shyps, ...} :: ths, Ss) =
      add_thms_shyps (ths, shyps union Ss);


(*get 'dangling' sort constraints of a thm*)
fun extra_shyps (th as Thm {shyps, ...}) =
  shyps \\ add_thm_sorts (th, []);


(* fix_shyps *)

(*preserve sort contexts of rule premises and substituted types*)
fun fix_shyps thms Ts thm =
  let
    val Thm {sign, der, maxidx, hyps, prop, ...} = thm;
    val shyps =
      add_thm_sorts (thm, add_typs_sorts (Ts, add_thms_shyps (thms, [])));
  in
    Thm {sign = sign, 
	 der = der,		(*No new derivation, as other rules call this*)
	 maxidx = maxidx,
	 shyps = shyps, hyps = hyps, prop = prop}
  end;


(* strip_shyps *)       (* FIXME improve? (e.g. only minimal extra sorts) *)

val force_strip_shyps = ref true;  (* FIXME tmp *)

(*remove extra sorts that are known to be syntactically non-empty*)
fun strip_shyps thm =
  let
    val Thm {sign, der, maxidx, shyps, hyps, prop} = thm;
    val sorts = add_thm_sorts (thm, []);
    val maybe_empty = not o Sign.nonempty_sort sign sorts;
    val shyps' = filter (fn S => S mem sorts orelse maybe_empty S) shyps;
  in
    Thm {sign = sign, der = der, maxidx = maxidx,
	 shyps =
	 (if eq_set (shyps',sorts) orelse not (!force_strip_shyps) then shyps'
	  else    (* FIXME tmp *)
	      (writeln ("WARNING Removed sort hypotheses: " ^
			commas (map Type.str_of_sort (shyps' \\ sorts)));
	       writeln "WARNING Let's hope these sorts are non-empty!";
           sorts)),
      hyps = hyps, 
      prop = prop}
  end;


(* implies_intr_shyps *)

(*discharge all extra sort hypotheses*)
fun implies_intr_shyps thm =
  (case extra_shyps thm of
    [] => thm
  | xshyps =>
      let
        val Thm {sign, der, maxidx, shyps, hyps, prop} = thm;
        val shyps' = logicS ins (shyps \\ xshyps);
        val used_names = foldr add_term_tfree_names (prop :: hyps, []);
        val names =
          tl (variantlist (replicate (length xshyps + 1) "'", used_names));
        val tfrees = map (TFree o rpair logicS) names;

        fun mk_insort (T, S) = map (Logic.mk_inclass o pair T) S;
        val sort_hyps = flat (map2 mk_insort (tfrees, xshyps));
      in
        Thm {sign = sign, 
	     der = infer_derivs (Implies_intr_shyps, [der]), 
	     maxidx = maxidx, 
	     shyps = shyps',
	     hyps = hyps, 
	     prop = Logic.list_implies (sort_hyps, prop)}
      end);


(** Axioms **)

(*look up the named axiom in the theory*)
fun get_axiom theory name =
  let
    fun get_ax [] = raise Match
      | get_ax (thy :: thys) =
	  let val {sign, new_axioms, parents, ...} = rep_theory thy
          in case Symtab.lookup (new_axioms, name) of
		Some t => fix_shyps [] []
		           (Thm {sign = sign, 
				 der = infer_derivs (Axiom(theory,name), []),
				 maxidx = maxidx_of_term t,
				 shyps = [], 
				 hyps = [], 
				 prop = t})
	      | None => get_ax parents handle Match => get_ax thys
          end;
  in
    get_ax [theory] handle Match
      => raise THEORY ("get_axiom: no axiom " ^ quote name, [theory])
  end;


(*return additional axioms of this theory node*)
fun axioms_of thy =
  map (fn (s, _) => (s, get_axiom thy s))
    (Symtab.dest (#new_axioms (rep_theory thy)));

fun name_thm (thy, name, th as Thm {sign, der, maxidx, shyps, hyps, prop}) = 
    if Sign.eq_sg (sign, sign_of thy) then
	Thm {sign = sign, 
	     der = Infer (Theorem(thy,name), [der]),
	     maxidx = maxidx,
	     shyps = shyps, 
	     hyps = hyps, 
	     prop = prop}
    else raise THM ("name_thm", 0, [th]);


(*Compression of theorems -- a separate rule, not integrated with the others,
  as it could be slow.*)
fun compress (Thm {sign, der, maxidx, shyps, hyps, prop}) = 
    Thm {sign = sign, 
	 der = der,	(*No derivation recorded!*)
	 maxidx = maxidx,
	 shyps = shyps, 
	 hyps = map Term.compress_term hyps, 
	 prop = Term.compress_term prop};


(*** Meta rules ***)

(* check that term does not contain same var with different typing/sorting *)
fun nodup_Vars(thm as Thm{prop,...}) s =
  Sign.nodup_Vars prop handle TYPE(msg,_,_) => raise THM(s^": "^msg,0,[thm]);

(** 'primitive' rules **)

(*discharge all assumptions t from ts*)
val disch = gen_rem (op aconv);

(*The assumption rule A|-A in a theory*)
fun assume ct : thm =
  let val {sign, t=prop, T, maxidx} = rep_cterm ct
  in  if T<>propT then
        raise THM("assume: assumptions must have type prop", 0, [])
      else if maxidx <> ~1 then
        raise THM("assume: assumptions may not contain scheme variables",
                  maxidx, [])
      else Thm{sign   = sign, 
	       der    = infer_derivs (Assume ct, []), 
	       maxidx = ~1, 
	       shyps  = add_term_sorts(prop,[]), 
	       hyps   = [prop], 
	       prop   = prop}
  end;

(*Implication introduction
  A |- B
  -------
  A ==> B
*)
fun implies_intr cA (thB as Thm{sign,der,maxidx,hyps,prop,...}) : thm =
  let val {sign=signA, t=A, T, maxidx=maxidxA} = rep_cterm cA
  in  if T<>propT then
        raise THM("implies_intr: assumptions must have type prop", 0, [thB])
      else fix_shyps [thB] []
        (Thm{sign = Sign.merge (sign,signA),  
	     der = infer_derivs (Implies_intr cA, [der]),
	     maxidx = max[maxidxA, maxidx],
	     shyps = [],
	     hyps = disch(hyps,A),
	     prop = implies$A$prop})
      handle TERM _ =>
        raise THM("implies_intr: incompatible signatures", 0, [thB])
  end;


(*Implication elimination
  A ==> B    A
  ------------
        B
*)
fun implies_elim thAB thA : thm =
    let val Thm{maxidx=maxA, der=derA, hyps=hypsA, prop=propA,...} = thA
        and Thm{sign, der, maxidx, hyps, prop,...} = thAB;
        fun err(a) = raise THM("implies_elim: "^a, 0, [thAB,thA])
    in  case prop of
            imp$A$B =>
                if imp=implies andalso  A aconv propA
                then fix_shyps [thAB, thA] []
                       (Thm{sign= merge_thm_sgs(thAB,thA),
			    der = infer_derivs (Implies_elim, [der,derA]),
			    maxidx = max[maxA,maxidx],
			    shyps = [],
			    hyps = hypsA union hyps,  (*dups suppressed*)
			    prop = B})
                else err("major premise")
          | _ => err("major premise")
    end;

(*Forall introduction.  The Free or Var x must not be free in the hypotheses.
    A
  -----
  !!x.A
*)
fun forall_intr cx (th as Thm{sign,der,maxidx,hyps,prop,...}) =
  let val x = term_of cx;
      fun result(a,T) = fix_shyps [th] []
        (Thm{sign = sign, 
	     der = infer_derivs (Forall_intr cx, [der]),
	     maxidx = maxidx,
	     shyps = [],
	     hyps = hyps,
	     prop = all(T) $ Abs(a, T, abstract_over (x,prop))})
  in  case x of
        Free(a,T) =>
          if exists (apl(x, Logic.occs)) hyps
          then  raise THM("forall_intr: variable free in assumptions", 0, [th])
          else  result(a,T)
      | Var((a,_),T) => result(a,T)
      | _ => raise THM("forall_intr: not a variable", 0, [th])
  end;

(*Forall elimination
  !!x.A
  ------
  A[t/x]
*)
fun forall_elim ct (th as Thm{sign,der,maxidx,hyps,prop,...}) : thm =
  let val {sign=signt, t, T, maxidx=maxt} = rep_cterm ct
  in  case prop of
          Const("all",Type("fun",[Type("fun",[qary,_]),_])) $ A =>
            if T<>qary then
                raise THM("forall_elim: type mismatch", 0, [th])
            else let val thm = fix_shyps [th] []
                      (Thm{sign= Sign.merge(sign,signt),
			   der = infer_derivs (Forall_elim ct, [der]),
                           maxidx = max[maxidx, maxt],
                           shyps = [],
			   hyps = hyps,  
			   prop = betapply(A,t)})
                 in nodup_Vars thm "forall_elim"; thm end
        | _ => raise THM("forall_elim: not quantified", 0, [th])
  end
  handle TERM _ =>
         raise THM("forall_elim: incompatible signatures", 0, [th]);


(* Equality *)

(* Definition of the relation =?= *)
val flexpair_def = fix_shyps [] []
  (Thm{sign= Sign.proto_pure, 
       der = Infer(Axiom(pure_thy, "flexpair_def"), []),
       shyps = [], 
       hyps = [], 
       maxidx = 0,
       prop = term_of (read_cterm Sign.proto_pure
		       ("(?t =?= ?u) == (?t == ?u::?'a::{})", propT))});

(*The reflexivity rule: maps  t   to the theorem   t==t   *)
fun reflexive ct =
  let val {sign, t, T, maxidx} = rep_cterm ct
  in  fix_shyps [] []
       (Thm{sign= sign, 
	    der = infer_derivs (Reflexive ct, []),
	    shyps = [],
	    hyps = [], 
	    maxidx = maxidx,
	    prop = Logic.mk_equals(t,t)})
  end;

(*The symmetry rule
  t==u
  ----
  u==t
*)
fun symmetric (th as Thm{sign,der,maxidx,shyps,hyps,prop}) =
  case prop of
      (eq as Const("==",_)) $ t $ u =>
        (*no fix_shyps*)
	  Thm{sign = sign,
	      der = infer_derivs (Symmetric, [der]),
	      maxidx = maxidx,
	      shyps = shyps,
	      hyps = hyps,
	      prop = eq$u$t}
    | _ => raise THM("symmetric", 0, [th]);

(*The transitive rule
  t1==u    u==t2
  --------------
      t1==t2
*)
fun transitive th1 th2 =
  let val Thm{der=der1, maxidx=max1, hyps=hyps1, prop=prop1,...} = th1
      and Thm{der=der2, maxidx=max2, hyps=hyps2, prop=prop2,...} = th2;
      fun err(msg) = raise THM("transitive: "^msg, 0, [th1,th2])
  in case (prop1,prop2) of
       ((eq as Const("==",_)) $ t1 $ u, Const("==",_) $ u' $ t2) =>
          if not (u aconv u') then err"middle term"  else
              fix_shyps [th1, th2] []
                (Thm{sign= merge_thm_sgs(th1,th2), 
		     der = infer_derivs (Transitive, [der1, der2]),
		     maxidx = max[max1,max2], 
		     shyps = [],
		     hyps = hyps1 union hyps2,
		     prop = eq$t1$t2})
     | _ =>  err"premises"
  end;

(*Beta-conversion: maps (%x.t)(u) to the theorem (%x.t)(u) == t[u/x] *)
fun beta_conversion ct =
  let val {sign, t, T, maxidx} = rep_cterm ct
  in  case t of
          Abs(_,_,bodt) $ u => fix_shyps [] []
            (Thm{sign = sign,  
		 der = infer_derivs (Beta_conversion ct, []),
		 maxidx = maxidx_of_term t,
		 shyps = [],
		 hyps = [],
		 prop = Logic.mk_equals(t, subst_bounds([u],bodt))})
        | _ =>  raise THM("beta_conversion: not a redex", 0, [])
  end;

(*The extensionality rule   (proviso: x not free in f, g, or hypotheses)
  f(x) == g(x)
  ------------
     f == g
*)
fun extensional (th as Thm{sign, der, maxidx,shyps,hyps,prop}) =
  case prop of
    (Const("==",_)) $ (f$x) $ (g$y) =>
      let fun err(msg) = raise THM("extensional: "^msg, 0, [th])
      in (if x<>y then err"different variables" else
          case y of
                Free _ =>
                  if exists (apl(y, Logic.occs)) (f::g::hyps)
                  then err"variable free in hyps or functions"    else  ()
              | Var _ =>
                  if Logic.occs(y,f)  orelse  Logic.occs(y,g)
                  then err"variable free in functions"   else  ()
              | _ => err"not a variable");
          (*no fix_shyps*)
          Thm{sign = sign,
	      der = infer_derivs (Extensional, [der]),
	      maxidx = maxidx,
	      shyps = shyps,
	      hyps = hyps, 
              prop = Logic.mk_equals(f,g)}
      end
 | _ =>  raise THM("extensional: premise", 0, [th]);

(*The abstraction rule.  The Free or Var x must not be free in the hypotheses.
  The bound variable will be named "a" (since x will be something like x320)
     t == u
  ------------
  %x.t == %x.u
*)
fun abstract_rule a cx (th as Thm{sign,der,maxidx,hyps,prop,...}) =
  let val x = term_of cx;
      val (t,u) = Logic.dest_equals prop
            handle TERM _ =>
                raise THM("abstract_rule: premise not an equality", 0, [th])
      fun result T = fix_shyps [th] []
	  (Thm{sign = sign,
	       der = infer_derivs (Abstract_rule (a,cx), [der]),
	       maxidx = maxidx, 
	       shyps = [], 
	       hyps = hyps,
	       prop = Logic.mk_equals(Abs(a, T, abstract_over (x,t)),
				      Abs(a, T, abstract_over (x,u)))})
  in  case x of
        Free(_,T) =>
         if exists (apl(x, Logic.occs)) hyps
         then raise THM("abstract_rule: variable free in assumptions", 0, [th])
         else result T
      | Var(_,T) => result T
      | _ => raise THM("abstract_rule: not a variable", 0, [th])
  end;

(*The combination rule
  f==g    t==u
  ------------
   f(t)==g(u)
*)
fun combination th1 th2 =
  let val Thm{der=der1, maxidx=max1, shyps=shyps1, hyps=hyps1, 
	      prop=prop1,...} = th1
      and Thm{der=der2, maxidx=max2, shyps=shyps2, hyps=hyps2, 
	      prop=prop2,...} = th2
  in case (prop1,prop2)  of
       (Const("==",_) $ f $ g, Const("==",_) $ t $ u) =>
          let val thm = (*no fix_shyps*)
             Thm{sign = merge_thm_sgs(th1,th2), 
		 der = infer_derivs (Combination, [der1, der2]),
                 maxidx = max[max1,max2], 
		 shyps = shyps1 union shyps2,
                 hyps = hyps1 union hyps2,
		 prop = Logic.mk_equals(f$t, g$u)}
          in nodup_Vars thm "combination"; thm end
     | _ =>  raise THM("combination: premises", 0, [th1,th2])
  end;


(* Equality introduction
  A==>B    B==>A
  --------------
       A==B
*)
fun equal_intr th1 th2 =
  let val Thm{der=der1,maxidx=max1, shyps=shyps1, hyps=hyps1, 
	      prop=prop1,...} = th1
      and Thm{der=der2, maxidx=max2, shyps=shyps2, hyps=hyps2, 
	      prop=prop2,...} = th2;
      fun err(msg) = raise THM("equal_intr: "^msg, 0, [th1,th2])
  in case (prop1,prop2) of
       (Const("==>",_) $ A $ B, Const("==>",_) $ B' $ A')  =>
	  if A aconv A' andalso B aconv B'
	  then
	    (*no fix_shyps*)
	      Thm{sign = merge_thm_sgs(th1,th2),
		  der = infer_derivs (Equal_intr, [der1, der2]),
		  maxidx = max[max1,max2],
		  shyps = shyps1 union shyps2,
		  hyps = hyps1 union hyps2,
		  prop = Logic.mk_equals(A,B)}
	  else err"not equal"
     | _ =>  err"premises"
  end;


(*The equal propositions rule
  A==B    A
  ---------
      B
*)
fun equal_elim th1 th2 =
  let val Thm{der=der1, maxidx=max1, hyps=hyps1, prop=prop1,...} = th1
      and Thm{der=der2, maxidx=max2, hyps=hyps2, prop=prop2,...} = th2;
      fun err(msg) = raise THM("equal_elim: "^msg, 0, [th1,th2])
  in  case prop1  of
       Const("==",_) $ A $ B =>
          if not (prop2 aconv A) then err"not equal"  else
            fix_shyps [th1, th2] []
              (Thm{sign= merge_thm_sgs(th1,th2), 
		   der = infer_derivs (Equal_elim, [der1, der2]),
		   maxidx = max[max1,max2],
		   shyps = [],
		   hyps = hyps1 union hyps2,
		   prop = B})
     | _ =>  err"major premise"
  end;



(**** Derived rules ****)

(*Discharge all hypotheses.  Need not verify cterms or call fix_shyps.
  Repeated hypotheses are discharged only once;  fold cannot do this*)
fun implies_intr_hyps (Thm{sign, der, maxidx, shyps, hyps=A::As, prop}) =
      implies_intr_hyps (*no fix_shyps*)
            (Thm{sign = sign, 
		 der = infer_derivs (Implies_intr_hyps, [der]), 
		 maxidx = maxidx, 
		 shyps = shyps,
                 hyps = disch(As,A),  
		 prop = implies$A$prop})
  | implies_intr_hyps th = th;

(*Smash" unifies the list of term pairs leaving no flex-flex pairs.
  Instantiates the theorem and deletes trivial tpairs.
  Resulting sequence may contain multiple elements if the tpairs are
    not all flex-flex. *)
fun flexflex_rule (th as Thm{sign, der, maxidx, hyps, prop,...}) =
  let fun newthm env =
          if Envir.is_empty env then th
          else
          let val (tpairs,horn) =
                        Logic.strip_flexpairs (Envir.norm_term env prop)
                (*Remove trivial tpairs, of the form t=t*)
              val distpairs = filter (not o op aconv) tpairs
              val newprop = Logic.list_flexpairs(distpairs, horn)
          in  fix_shyps [th] (env_codT env)
                (Thm{sign = sign, 
		     der = infer_derivs (Flexflex_rule env, [der]), 
		     maxidx = maxidx_of_term newprop, 
		     shyps = [], 
		     hyps = hyps,
		     prop = newprop})
          end;
      val (tpairs,_) = Logic.strip_flexpairs prop
  in Sequence.maps newthm
            (Unify.smash_unifiers(sign, Envir.empty maxidx, tpairs))
  end;

(*Instantiation of Vars
           A
  -------------------
  A[t1/v1,....,tn/vn]
*)

(*Check that all the terms are Vars and are distinct*)
fun instl_ok ts = forall is_Var ts andalso null(findrep ts);

(*For instantiate: process pair of cterms, merge theories*)
fun add_ctpair ((ct,cu), (sign,tpairs)) =
  let val {sign=signt, t=t, T= T, ...} = rep_cterm ct
      and {sign=signu, t=u, T= U, ...} = rep_cterm cu
  in  if T=U  then (Sign.merge(sign, Sign.merge(signt, signu)), (t,u)::tpairs)
      else raise TYPE("add_ctpair", [T,U], [t,u])
  end;

fun add_ctyp ((v,ctyp), (sign',vTs)) =
  let val {T,sign} = rep_ctyp ctyp
  in (Sign.merge(sign,sign'), (v,T)::vTs) end;

(*Left-to-right replacements: ctpairs = [...,(vi,ti),...].
  Instantiates distinct Vars by terms of same type.
  Normalizes the new theorem! *)
fun instantiate ([], []) th = th
  | instantiate (vcTs,ctpairs)  (th as Thm{sign,der,maxidx,hyps,prop,...}) =
  let val (newsign,tpairs) = foldr add_ctpair (ctpairs, (sign,[]));
      val (newsign,vTs) = foldr add_ctyp (vcTs, (newsign,[]));
      val newprop =
            Envir.norm_term (Envir.empty 0)
              (subst_atomic tpairs
               (Type.inst_term_tvars(#tsig(Sign.rep_sg newsign),vTs) prop))
      val newth =
            fix_shyps [th] (map snd vTs)
              (Thm{sign = newsign, 
		   der = infer_derivs (Instantiate(vcTs,ctpairs), [der]), 
		   maxidx = maxidx_of_term newprop, 
		   shyps = [],
		   hyps = hyps,
		   prop = newprop})
  in  if not(instl_ok(map #1 tpairs))
      then raise THM("instantiate: variables not distinct", 0, [th])
      else if not(null(findrep(map #1 vTs)))
      then raise THM("instantiate: type variables not distinct", 0, [th])
      else nodup_Vars newth "instantiate";
      newth
  end
  handle TERM _ =>
           raise THM("instantiate: incompatible signatures",0,[th])
       | TYPE _ => raise THM("instantiate: type conflict", 0, [th]);

(*The trivial implication A==>A, justified by assume and forall rules.
  A can contain Vars, not so for assume!   *)
fun trivial ct : thm =
  let val {sign, t=A, T, maxidx} = rep_cterm ct
  in  if T<>propT then
            raise THM("trivial: the term must have type prop", 0, [])
      else fix_shyps [] []
        (Thm{sign = sign, 
	     der = infer_derivs (Trivial ct, []), 
	     maxidx = maxidx, 
	     shyps = [], 
	     hyps = [],
	     prop = implies$A$A})
  end;

(*Axiom-scheme reflecting signature contents: "OFCLASS(?'a::c, c_class)" *)
fun class_triv thy c =
  let val sign = sign_of thy;
      val Cterm {t, maxidx, ...} =
	  cterm_of sign (Logic.mk_inclass (TVar (("'a", 0), [c]), c))
	    handle TERM (msg, _) => raise THM ("class_triv: " ^ msg, 0, []);
  in
    fix_shyps [] []
      (Thm {sign = sign, 
	    der = infer_derivs (Class_triv(thy,c), []), 
	    maxidx = maxidx, 
	    shyps = [], 
	    hyps = [], 
	    prop = t})
  end;


(* Replace all TFrees not in the hyps by new TVars *)
fun varifyT(Thm{sign,der,maxidx,shyps,hyps,prop}) =
  let val tfrees = foldr add_term_tfree_names (hyps,[])
  in (*no fix_shyps*)
    Thm{sign = sign, 
	der = infer_derivs (VarifyT, [der]), 
	maxidx = max[0,maxidx], 
	shyps = shyps, 
	hyps = hyps,
        prop = Type.varify(prop,tfrees)}
  end;

(* Replace all TVars by new TFrees *)
fun freezeT(Thm{sign,der,maxidx,shyps,hyps,prop}) =
  let val prop' = Type.freeze prop
  in (*no fix_shyps*)
    Thm{sign = sign, 
	der = infer_derivs (FreezeT, [der]),
	maxidx = maxidx_of_term prop',
	shyps = shyps,
	hyps = hyps,
        prop = prop'}
  end;


(*** Inference rules for tactics ***)

(*Destruct proof state into constraints, other goals, goal(i), rest *)
fun dest_state (state as Thm{prop,...}, i) =
  let val (tpairs,horn) = Logic.strip_flexpairs prop
  in  case  Logic.strip_prems(i, [], horn) of
          (B::rBs, C) => (tpairs, rev rBs, B, C)
        | _ => raise THM("dest_state", i, [state])
  end
  handle TERM _ => raise THM("dest_state", i, [state]);

(*Increment variables and parameters of orule as required for
  resolution with goal i of state. *)
fun lift_rule (state, i) orule =
  let val Thm{shyps=sshyps, prop=sprop, maxidx=smax, sign=ssign,...} = state
      val (Bi::_, _) = Logic.strip_prems(i, [], Logic.skip_flexpairs sprop)
        handle TERM _ => raise THM("lift_rule", i, [orule,state])
      val ct_Bi = Cterm {sign=ssign, maxidx=smax, T=propT, t=Bi}
      val (lift_abs,lift_all) = Logic.lift_fns(Bi,smax+1)
      val (Thm{sign, der, maxidx,shyps,hyps,prop}) = orule
      val (tpairs,As,B) = Logic.strip_horn prop
  in  (*no fix_shyps*)
      Thm{sign = merge_thm_sgs(state,orule),
	  der = infer_derivs (Lift_rule(ct_Bi, i), [der]),
	  maxidx = maxidx+smax+1,
          shyps=sshyps union shyps, 
	  hyps=hyps, 
          prop = Logic.rule_of (map (pairself lift_abs) tpairs,
				map lift_all As,    
				lift_all B)}
  end;

(*Solve subgoal Bi of proof state B1...Bn/C by assumption. *)
fun assumption i state =
  let val Thm{sign,der,maxidx,hyps,prop,...} = state;
      val (tpairs, Bs, Bi, C) = dest_state(state,i)
      fun newth (env as Envir.Envir{maxidx, ...}, tpairs) =
        fix_shyps [state] (env_codT env)
          (Thm{sign = sign, 
	       der = infer_derivs (Assumption (i, Some env), [der]),
	       maxidx = maxidx,
	       shyps = [],
	       hyps = hyps,
	       prop = 
	       if Envir.is_empty env then (*avoid wasted normalizations*)
		   Logic.rule_of (tpairs, Bs, C)
	       else (*normalize the new rule fully*)
		   Envir.norm_term env (Logic.rule_of (tpairs, Bs, C))});
      fun addprfs [] = Sequence.null
        | addprfs ((t,u)::apairs) = Sequence.seqof (fn()=> Sequence.pull
             (Sequence.mapp newth
                (Unify.unifiers(sign,Envir.empty maxidx, (t,u)::tpairs))
                (addprfs apairs)))
  in  addprfs (Logic.assum_pairs Bi)  end;

(*Solve subgoal Bi of proof state B1...Bn/C by assumption.
  Checks if Bi's conclusion is alpha-convertible to one of its assumptions*)
fun eq_assumption i state =
  let val Thm{sign,der,maxidx,hyps,prop,...} = state;
      val (tpairs, Bs, Bi, C) = dest_state(state,i)
  in  if exists (op aconv) (Logic.assum_pairs Bi)
      then fix_shyps [state] []
             (Thm{sign = sign, 
		  der = infer_derivs (Assumption (i,None), [der]),
		  maxidx = maxidx,
		  shyps = [],
		  hyps = hyps,
		  prop = Logic.rule_of(tpairs, Bs, C)})
      else  raise THM("eq_assumption", 0, [state])
  end;


(** User renaming of parameters in a subgoal **)

(*Calls error rather than raising an exception because it is intended
  for top-level use -- exception handling would not make sense here.
  The names in cs, if distinct, are used for the innermost parameters;
   preceding parameters may be renamed to make all params distinct.*)
fun rename_params_rule (cs, i) state =
  let val Thm{sign,der,maxidx,hyps,prop,...} = state
      val (tpairs, Bs, Bi, C) = dest_state(state,i)
      val iparams = map #1 (Logic.strip_params Bi)
      val short = length iparams - length cs
      val newnames =
            if short<0 then error"More names than abstractions!"
            else variantlist(take (short,iparams), cs) @ cs
      val freenames = map (#1 o dest_Free) (term_frees prop)
      val newBi = Logic.list_rename_params (newnames, Bi)
  in
  case findrep cs of
     c::_ => error ("Bound variables not distinct: " ^ c)
   | [] => (case cs inter freenames of
       a::_ => error ("Bound/Free variable clash: " ^ a)
     | [] => fix_shyps [state] []
		(Thm{sign = sign,
		     der = infer_derivs (Rename_params_rule(cs,i), [der]),
		     maxidx = maxidx,
		     shyps = [],
		     hyps = hyps,
		     prop = Logic.rule_of(tpairs, Bs@[newBi], C)}))
  end;

(*** Preservation of bound variable names ***)

(*Scan a pair of terms; while they are similar,
  accumulate corresponding bound vars in "al"*)
fun match_bvs(Abs(x,_,s),Abs(y,_,t), al) =
      match_bvs(s, t, if x="" orelse y="" then al
                                          else (x,y)::al)
  | match_bvs(f$s, g$t, al) = match_bvs(f,g,match_bvs(s,t,al))
  | match_bvs(_,_,al) = al;

(* strip abstractions created by parameters *)
fun match_bvars((s,t),al) = match_bvs(strip_abs_body s, strip_abs_body t, al);


(* strip_apply f A(,B) strips off all assumptions/parameters from A
   introduced by lifting over B, and applies f to remaining part of A*)
fun strip_apply f =
  let fun strip(Const("==>",_)$ A1 $ B1,
                Const("==>",_)$ _  $ B2) = implies $ A1 $ strip(B1,B2)
        | strip((c as Const("all",_)) $ Abs(a,T,t1),
                      Const("all",_)  $ Abs(_,_,t2)) = c$Abs(a,T,strip(t1,t2))
        | strip(A,_) = f A
  in strip end;

(*Use the alist to rename all bound variables and some unknowns in a term
  dpairs = current disagreement pairs;  tpairs = permanent ones (flexflex);
  Preserves unknowns in tpairs and on lhs of dpairs. *)
fun rename_bvs([],_,_,_) = I
  | rename_bvs(al,dpairs,tpairs,B) =
    let val vars = foldr add_term_vars
                        (map fst dpairs @ map fst tpairs @ map snd tpairs, [])
        (*unknowns appearing elsewhere be preserved!*)
        val vids = map (#1 o #1 o dest_Var) vars;
        fun rename(t as Var((x,i),T)) =
                (case assoc(al,x) of
                   Some(y) => if x mem vids orelse y mem vids then t
                              else Var((y,i),T)
                 | None=> t)
          | rename(Abs(x,T,t)) =
              Abs(case assoc(al,x) of Some(y) => y | None => x,
                  T, rename t)
          | rename(f$t) = rename f $ rename t
          | rename(t) = t;
        fun strip_ren Ai = strip_apply rename (Ai,B)
    in strip_ren end;

(*Function to rename bounds/unknowns in the argument, lifted over B*)
fun rename_bvars(dpairs, tpairs, B) =
        rename_bvs(foldr match_bvars (dpairs,[]), dpairs, tpairs, B);


(*** RESOLUTION ***)

(** Lifting optimizations **)

(*strip off pairs of assumptions/parameters in parallel -- they are
  identical because of lifting*)
fun strip_assums2 (Const("==>", _) $ _ $ B1,
                   Const("==>", _) $ _ $ B2) = strip_assums2 (B1,B2)
  | strip_assums2 (Const("all",_)$Abs(a,T,t1),
                   Const("all",_)$Abs(_,_,t2)) =
      let val (B1,B2) = strip_assums2 (t1,t2)
      in  (Abs(a,T,B1), Abs(a,T,B2))  end
  | strip_assums2 BB = BB;


(*Faster normalization: skip assumptions that were lifted over*)
fun norm_term_skip env 0 t = Envir.norm_term env t
  | norm_term_skip env n (Const("all",_)$Abs(a,T,t)) =
        let val Envir.Envir{iTs, ...} = env
            val T' = typ_subst_TVars iTs T
            (*Must instantiate types of parameters because they are flattened;
              this could be a NEW parameter*)
        in  all T' $ Abs(a, T', norm_term_skip env n t)  end
  | norm_term_skip env n (Const("==>", _) $ A $ B) =
        implies $ A $ norm_term_skip env (n-1) B
  | norm_term_skip env n t = error"norm_term_skip: too few assumptions??";


(*Composition of object rule r=(A1...Am/B) with proof state s=(B1...Bn/C)
  Unifies B with Bi, replacing subgoal i    (1 <= i <= n)
  If match then forbid instantiations in proof state
  If lifted then shorten the dpair using strip_assums2.
  If eres_flg then simultaneously proves A1 by assumption.
  nsubgoal is the number of new subgoals (written m above).
  Curried so that resolution calls dest_state only once.
*)
local open Sequence; exception COMPOSE
in
fun bicompose_aux match (state, (stpairs, Bs, Bi, C), lifted)
                        (eres_flg, orule, nsubgoal) =
 let val Thm{der=sder, maxidx=smax, shyps=sshyps, hyps=shyps, ...} = state
     and Thm{der=rder, maxidx=rmax, shyps=rshyps, hyps=rhyps, 
	     prop=rprop,...} = orule
         (*How many hyps to skip over during normalization*)
     and nlift = Logic.count_prems(strip_all_body Bi,
                                   if eres_flg then ~1 else 0)
     val sign = merge_thm_sgs(state,orule);
     (** Add new theorem with prop = '[| Bs; As |] ==> C' to thq **)
     fun addth As ((env as Envir.Envir {maxidx, ...}, tpairs), thq) =
       let val normt = Envir.norm_term env;
           (*perform minimal copying here by examining env*)
           val normp =
             if Envir.is_empty env then (tpairs, Bs @ As, C)
             else
             let val ntps = map (pairself normt) tpairs
             in if the (Envir.minidx env) > smax then
                  (*no assignments in state; normalize the rule only*)
                  if lifted
                  then (ntps, Bs @ map (norm_term_skip env nlift) As, C)
                  else (ntps, Bs @ map normt As, C)
                else if match then raise COMPOSE
                else (*normalize the new rule fully*)
                  (ntps, map normt (Bs @ As), normt C)
             end
           val th = (*tuned fix_shyps*)
             Thm{sign = sign,
		 der = infer_derivs (Bicompose(match, eres_flg,
					       1 + length Bs, nsubgoal, env),
				     [rder,sder]),
		 maxidx = maxidx,
		 shyps = add_env_sorts (env, rshyps union sshyps),
		 hyps = rhyps union shyps,
		 prop = Logic.rule_of normp}
        in  cons(th, thq)  end  handle COMPOSE => thq
     val (rtpairs,rhorn) = Logic.strip_flexpairs(rprop);
     val (rAs,B) = Logic.strip_prems(nsubgoal, [], rhorn)
       handle TERM _ => raise THM("bicompose: rule", 0, [orule,state]);
     (*Modify assumptions, deleting n-th if n>0 for e-resolution*)
     fun newAs(As0, n, dpairs, tpairs) =
       let val As1 = if !Logic.auto_rename orelse not lifted then As0
                     else map (rename_bvars(dpairs,tpairs,B)) As0
       in (map (Logic.flatten_params n) As1)
          handle TERM _ =>
          raise THM("bicompose: 1st premise", 0, [orule])
       end;
     val env = Envir.empty(max[rmax,smax]);
     val BBi = if lifted then strip_assums2(B,Bi) else (B,Bi);
     val dpairs = BBi :: (rtpairs@stpairs);
     (*elim-resolution: try each assumption in turn.  Initially n=1*)
     fun tryasms (_, _, []) = null
       | tryasms (As, n, (t,u)::apairs) =
          (case pull(Unify.unifiers(sign, env, (t,u)::dpairs))  of
               None                   => tryasms (As, n+1, apairs)
             | cell as Some((_,tpairs),_) =>
                   its_right (addth (newAs(As, n, [BBi,(u,t)], tpairs)))
                       (seqof (fn()=> cell),
                        seqof (fn()=> pull (tryasms (As, n+1, apairs)))));
     fun eres [] = raise THM("bicompose: no premises", 0, [orule,state])
       | eres (A1::As) = tryasms (As, 1, Logic.assum_pairs A1);
     (*ordinary resolution*)
     fun res(None) = null
       | res(cell as Some((_,tpairs),_)) =
             its_right (addth(newAs(rev rAs, 0, [BBi], tpairs)))
                       (seqof (fn()=> cell), null)
 in  if eres_flg then eres(rev rAs)
     else res(pull(Unify.unifiers(sign, env, dpairs)))
 end;
end;  (*open Sequence*)


fun bicompose match arg i state =
    bicompose_aux match (state, dest_state(state,i), false) arg;

(*Quick test whether rule is resolvable with the subgoal with hyps Hs
  and conclusion B.  If eres_flg then checks 1st premise of rule also*)
fun could_bires (Hs, B, eres_flg, rule) =
    let fun could_reshyp (A1::_) = exists (apl(A1,could_unify)) Hs
          | could_reshyp [] = false;  (*no premise -- illegal*)
    in  could_unify(concl_of rule, B) andalso
        (not eres_flg  orelse  could_reshyp (prems_of rule))
    end;

(*Bi-resolution of a state with a list of (flag,rule) pairs.
  Puts the rule above:  rule/state.  Renames vars in the rules. *)
fun biresolution match brules i state =
    let val lift = lift_rule(state, i);
        val (stpairs, Bs, Bi, C) = dest_state(state,i)
        val B = Logic.strip_assums_concl Bi;
        val Hs = Logic.strip_assums_hyp Bi;
        val comp = bicompose_aux match (state, (stpairs, Bs, Bi, C), true);
        fun res [] = Sequence.null
          | res ((eres_flg, rule)::brules) =
              if could_bires (Hs, B, eres_flg, rule)
              then Sequence.seqof (*delay processing remainder till needed*)
                  (fn()=> Some(comp (eres_flg, lift rule, nprems_of rule),
                               res brules))
              else res brules
    in  Sequence.flats (res brules)  end;



(*** Meta simp sets ***)

type rrule = {thm:thm, lhs:term, perm:bool};
type cong = {thm:thm, lhs:term};
datatype meta_simpset =
  Mss of {net:rrule Net.net, congs:(string * cong)list, bounds:string list,
          prems: thm list, mk_rews: thm -> thm list};

(*A "mss" contains data needed during conversion:
  net: discrimination net of rewrite rules
  congs: association list of congruence rules
  bounds: names of bound variables already used;
          for generating new names when rewriting under lambda abstractions
  mk_rews: used when local assumptions are added
*)

val empty_mss = Mss{net = Net.empty, congs = [], bounds=[], prems = [],
                    mk_rews = K[]};

exception SIMPLIFIER of string * thm;

fun prtm a sign t = (writeln a; writeln(Sign.string_of_term sign t));

val trace_simp = ref false;

fun trace_term a sign t = if !trace_simp then prtm a sign t else ();

fun trace_thm a (Thm{sign,prop,...}) = trace_term a sign prop;

fun vperm(Var _, Var _) = true
  | vperm(Abs(_,_,s), Abs(_,_,t)) = vperm(s,t)
  | vperm(t1$t2, u1$u2) = vperm(t1,u1) andalso vperm(t2,u2)
  | vperm(t,u) = (t=u);

fun var_perm(t,u) = vperm(t,u) andalso
                    eq_set(add_term_vars(t,[]), add_term_vars(u,[]))

(*simple test for looping rewrite*)
fun loops sign prems (lhs,rhs) =
   is_Var(lhs)
  orelse
   (exists (apl(lhs, Logic.occs)) (rhs::prems))
  orelse
   (null(prems) andalso
    Pattern.matches (#tsig(Sign.rep_sg sign)) (lhs,rhs));
(* the condition "null(prems)" in the last case is necessary because
   conditional rewrites with extra variables in the conditions may terminate
   although the rhs is an instance of the lhs. Example:
   ?m < ?n ==> f(?n) == f(?m)
*)

fun mk_rrule raw_thm =
  let
      val thm = strip_shyps raw_thm;
      val Thm{sign,prop,maxidx,...} = thm;
      val prems = Logic.strip_imp_prems prop
      val concl = Logic.strip_imp_concl prop
      val (lhs,_) = Logic.dest_equals concl handle TERM _ =>
                      raise SIMPLIFIER("Rewrite rule not a meta-equality",thm)
      val econcl = Pattern.eta_contract concl
      val (elhs,erhs) = Logic.dest_equals econcl
      val perm = var_perm(elhs,erhs) andalso not(elhs aconv erhs)
                                     andalso not(is_Var(elhs))
  in
     if not perm andalso loops sign prems (elhs,erhs) then
       (prtm "Warning: ignoring looping rewrite rule" sign prop; None)
     else Some{thm=thm,lhs=lhs,perm=perm}
  end;

local
 fun eq({thm=Thm{prop=p1,...},...}:rrule,
        {thm=Thm{prop=p2,...},...}:rrule) = p1 aconv p2
in

fun add_simp(mss as Mss{net,congs,bounds,prems,mk_rews},
             thm as Thm{sign,prop,...}) =
  case mk_rrule thm of
    None => mss
  | Some(rrule as {lhs,...}) =>
      (trace_thm "Adding rewrite rule:" thm;
       Mss{net = (Net.insert_term((lhs,rrule),net,eq)
                 handle Net.INSERT =>
                  (prtm "Warning: ignoring duplicate rewrite rule" sign prop;
                   net)),
           congs=congs, bounds=bounds, prems=prems,mk_rews=mk_rews});

fun del_simp(mss as Mss{net,congs,bounds,prems,mk_rews},
             thm as Thm{sign,prop,...}) =
  case mk_rrule thm of
    None => mss
  | Some(rrule as {lhs,...}) =>
      Mss{net = (Net.delete_term((lhs,rrule),net,eq)
                handle Net.INSERT =>
                 (prtm "Warning: rewrite rule not in simpset" sign prop;
                  net)),
             congs=congs, bounds=bounds, prems=prems,mk_rews=mk_rews}

end;

val add_simps = foldl add_simp;
val del_simps = foldl del_simp;

fun mss_of thms = add_simps(empty_mss,thms);

fun add_cong(Mss{net,congs,bounds,prems,mk_rews},thm) =
  let val (lhs,_) = Logic.dest_equals(concl_of thm) handle TERM _ =>
                    raise SIMPLIFIER("Congruence not a meta-equality",thm)
(*      val lhs = Pattern.eta_contract lhs*)
      val (a,_) = dest_Const (head_of lhs) handle TERM _ =>
                  raise SIMPLIFIER("Congruence must start with a constant",thm)
  in Mss{net=net, congs=(a,{lhs=lhs,thm=thm})::congs, bounds=bounds,
         prems=prems, mk_rews=mk_rews}
  end;

val (op add_congs) = foldl add_cong;

fun add_prems(Mss{net,congs,bounds,prems,mk_rews},thms) =
  Mss{net=net, congs=congs, bounds=bounds, prems=thms@prems, mk_rews=mk_rews};

fun prems_of_mss(Mss{prems,...}) = prems;

fun set_mk_rews(Mss{net,congs,bounds,prems,...},mk_rews) =
  Mss{net=net, congs=congs, bounds=bounds, prems=prems, mk_rews=mk_rews};
fun mk_rews_of_mss(Mss{mk_rews,...}) = mk_rews;


(*** Meta-level rewriting
     uses conversions, omitting proofs for efficiency.  See
        L C Paulson, A higher-order implementation of rewriting,
        Science of Computer Programming 3 (1983), pages 119-149. ***)

type prover = meta_simpset -> thm -> thm option;
type termrec = (Sign.sg * term list) * term;
type conv = meta_simpset -> termrec -> termrec;

datatype order = LESS | EQUAL | GREATER;

fun stringord(a,b:string) = if a<b then LESS  else
                            if a=b then EQUAL else GREATER;

fun intord(i,j:int) = if i<j then LESS  else
                      if i=j then EQUAL else GREATER;

(* NB: non-linearity of the ordering is not a soundness problem *)

(* FIXME: "***ABSTRACTION***" is a hack and makes the ordering non-linear *)
fun string_of_hd(Const(a,_)) = a
  | string_of_hd(Free(a,_))  = a
  | string_of_hd(Var(v,_))   = Syntax.string_of_vname v
  | string_of_hd(Bound i)    = string_of_int i
  | string_of_hd(Abs _)      = "***ABSTRACTION***";

(* a strict (not reflexive) linear well-founded AC-compatible ordering
 * for terms:
 * s < t <=> 1. size(s) < size(t) or
             2. size(s) = size(t) and s=f(...) and t = g(...) and f<g or
             3. size(s) = size(t) and s=f(s1..sn) and t=f(t1..tn) and
                (s1..sn) < (t1..tn) (lexicographically)
 *)

(* FIXME: should really take types into account as well.
 * Otherwise non-linear *)
fun termord(Abs(_,_,t),Abs(_,_,u)) = termord(t,u)
  | termord(t,u) =
      (case intord(size_of_term t,size_of_term u) of
         EQUAL => let val (f,ts) = strip_comb t and (g,us) = strip_comb u
                  in case stringord(string_of_hd f, string_of_hd g) of
                       EQUAL => lextermord(ts,us)
                     | ord   => ord
                  end
       | ord => ord)
and lextermord(t::ts,u::us) =
      (case termord(t,u) of
         EQUAL => lextermord(ts,us)
       | ord   => ord)
  | lextermord([],[]) = EQUAL
  | lextermord _ = error("lextermord");

fun termless tu = (termord tu = LESS);

fun check_conv (thm as Thm{shyps,hyps,prop,sign,der,maxidx,...}, prop0, ders) =
  let fun err() = (trace_thm "Proved wrong thm (Check subgoaler?)" thm;
                   trace_term "Should have proved" sign prop0;
                   None)
      val (lhs0,_) = Logic.dest_equals(Logic.strip_imp_concl prop0)
  in case prop of
       Const("==",_) $ lhs $ rhs =>
         if (lhs = lhs0) orelse
            (lhs aconv Envir.norm_term (Envir.empty 0) lhs0)
         then (trace_thm "SUCCEEDED" thm; 
	       Some(shyps, hyps, maxidx, rhs, der::ders))
         else err()
     | _ => err()
  end;

fun ren_inst(insts,prop,pat,obj) =
  let val ren = match_bvs(pat,obj,[])
      fun renAbs(Abs(x,T,b)) =
            Abs(case assoc(ren,x) of None => x | Some(y) => y, T, renAbs(b))
        | renAbs(f$t) = renAbs(f) $ renAbs(t)
        | renAbs(t) = t
  in subst_vars insts (if null(ren) then prop else renAbs(prop)) end;

fun add_insts_sorts ((iTs, is), Ss) =
  add_typs_sorts (map snd iTs, add_terms_sorts (map snd is, Ss));


(*Conversion to apply the meta simpset to a term*)
fun rewritec (prover,signt) (mss as Mss{net,...}) 
             (shypst,hypst,maxidxt,t,ders) =
  let val etat = Pattern.eta_contract t;
      fun rew {thm as Thm{sign,der,maxidx,shyps,hyps,prop,...}, lhs, perm} =
        let val unit = if Sign.subsig(sign,signt) then ()
                  else (trace_thm"Warning: rewrite rule from different theory"
                          thm;
                        raise Pattern.MATCH)
            val rprop = if maxidxt = ~1 then prop
                        else Logic.incr_indexes([],maxidxt+1) prop;
            val rlhs = if maxidxt = ~1 then lhs
                       else fst(Logic.dest_equals(Logic.strip_imp_concl rprop))
            val insts = Pattern.match (#tsig(Sign.rep_sg signt)) (rlhs,etat)
            val prop' = ren_inst(insts,rprop,rlhs,t);
            val hyps' = hyps union hypst;
            val shyps' = add_insts_sorts (insts, shyps union shypst);
            val maxidx' = maxidx_of_term prop'
            val ct' = Cterm{sign = signt,	(*used for deriv only*)
			    t = prop',
			    T = propT,
			    maxidx = maxidx'}
	    val der' = infer_derivs (RewriteC ct', [der])
            val thm' = Thm{sign = signt, 
			   der = der',
			   shyps = shyps',
			   hyps = hyps',
                           prop = prop',
			   maxidx = maxidx'}
            val (lhs',rhs') = Logic.dest_equals(Logic.strip_imp_concl prop')
        in if perm andalso not(termless(rhs',lhs')) then None else
           if Logic.count_prems(prop',0) = 0
           then (trace_thm "Rewriting:" thm'; 
		 Some(shyps', hyps', maxidx', rhs', der'::ders))
           else (trace_thm "Trying to rewrite:" thm';
                 case prover mss thm' of
                   None       => (trace_thm "FAILED" thm'; None)
                 | Some(thm2) => check_conv(thm2,prop',ders))
        end

      fun rews [] = None
        | rews (rrule::rrules) =
            let val opt = rew rrule handle Pattern.MATCH => None
            in case opt of None => rews rrules | some => some end;

  in case etat of
       Abs(_,_,body) $ u => Some(shypst, hypst, maxidxt, 
				 subst_bounds([u], body),
				 ders)
     | _                 => rews(Net.match_term net etat)
  end;

(*Conversion to apply a congruence rule to a term*)
fun congc (prover,signt) {thm=cong,lhs=lhs} (shypst,hypst,maxidxt,t,ders) =
  let val Thm{sign,der,shyps,hyps,maxidx,prop,...} = cong
      val unit = if Sign.subsig(sign,signt) then ()
                 else error("Congruence rule from different theory")
      val tsig = #tsig(Sign.rep_sg signt)
      val rprop = if maxidxt = ~1 then prop
                  else Logic.incr_indexes([],maxidxt+1) prop;
      val rlhs = if maxidxt = ~1 then lhs
                 else fst(Logic.dest_equals(Logic.strip_imp_concl rprop))
      val insts = Pattern.match tsig (rlhs,t)
      (* Pattern.match can raise Pattern.MATCH;
         is handled when congc is called *)
      val prop' = ren_inst(insts,rprop,rlhs,t);
      val shyps' = add_insts_sorts (insts, shyps union shypst)
      val maxidx' = maxidx_of_term prop'
      val ct' = Cterm{sign = signt,	(*used for deriv only*)
		      t = prop',
		      T = propT,
		      maxidx = maxidx'}
      val thm' = Thm{sign = signt, 
		     der = infer_derivs (CongC ct', [der]),
		     shyps = shyps',
		     hyps = hyps union hypst,
                     prop = prop',
		     maxidx = maxidx'};
      val unit = trace_thm "Applying congruence rule" thm';
      fun err() = error("Failed congruence proof!")

  in case prover thm' of
       None => err()
     | Some(thm2) => (case check_conv(thm2,prop',ders) of
                        None => err() | some => some)
  end;



fun bottomc ((simprem,useprem),prover,sign) =
 let fun botc fail mss trec =
	  (case subc mss trec of
	     some as Some(trec1) =>
	       (case rewritec (prover,sign) mss trec1 of
		  Some(trec2) => botc false mss trec2
		| None => some)
	   | None =>
	       (case rewritec (prover,sign) mss trec of
		  Some(trec2) => botc false mss trec2
		| None => if fail then None else Some(trec)))

     and try_botc mss trec = (case botc true mss trec of
				Some(trec1) => trec1
			      | None => trec)

     and subc (mss as Mss{net,congs,bounds,prems,mk_rews})
	      (trec as (shyps,hyps,maxidx,t0,ders)) =
       (case t0 of
	   Abs(a,T,t) =>
	     let val b = variant bounds a
		 val v = Free("." ^ b,T)
		 val mss' = Mss{net=net, congs=congs, bounds=b::bounds,
				prems=prems,mk_rews=mk_rews}
	     in case botc true mss' 
		       (shyps,hyps,maxidx,subst_bounds([v],t),ders) of
		  Some(shyps',hyps',maxidx',t',ders') =>
		    Some(shyps', hyps', maxidx',
			 Abs(a, T, abstract_over(v,t')),
			 ders')
		| None => None
	     end
	 | t$u => (case t of
	     Const("==>",_)$s  => Some(impc(shyps,hyps,maxidx,s,u,mss,ders))
	   | Abs(_,_,body) =>
	       let val trec = (shyps,hyps,maxidx,subst_bounds([u],body),ders)
	       in case subc mss trec of
		    None => Some(trec)
		  | trec => trec
	       end
	   | _  =>
	       let fun appc() =
		     (case botc true mss (shyps,hyps,maxidx,t,ders) of
			Some(shyps1,hyps1,maxidx1,t1,ders1) =>
			  (case botc true mss (shyps1,hyps1,maxidx,u,ders1) of
			     Some(shyps2,hyps2,maxidx2,u1,ders2) =>
			       Some(shyps2, hyps2, max[maxidx1,maxidx2],
				    t1$u1, ders2)
			   | None =>
			       Some(shyps1, hyps1, max[maxidx1,maxidx], t1$u,
				    ders1))
		      | None =>
			  (case botc true mss (shyps,hyps,maxidx,u,ders) of
			     Some(shyps1,hyps1,maxidx1,u1,ders1) =>
			       Some(shyps1, hyps1, max[maxidx,maxidx1], 
				    t$u1, ders1)
			   | None => None))
		   val (h,ts) = strip_comb t
	       in case h of
		    Const(a,_) =>
		      (case assoc(congs,a) of
			 None => appc()
		       | Some(cong) => (congc (prover mss,sign) cong trec
                                        handle Pattern.MATCH => appc() ) )
		  | _ => appc()
	       end)
	 | _ => None)

     and impc(shyps, hyps, maxidx, s, u, mss as Mss{mk_rews,...}, ders) =
       let val (shyps1,hyps1,_,s1,ders1) =
	     if simprem then try_botc mss (shyps,hyps,maxidx,s,ders)
	                else (shyps,hyps,0,s,ders);
	   val maxidx1 = maxidx_of_term s1
	   val mss1 =
	     if not useprem orelse maxidx1 <> ~1 then mss
	     else let val thm = assume (Cterm{sign=sign, t=s1, 
					      T=propT, maxidx=maxidx1})
		  in add_simps(add_prems(mss,[thm]), mk_rews thm) end
	   val (shyps2,hyps2,maxidx2,u1,ders2) = 
	       try_botc mss1 (shyps1,hyps1,maxidx,u,ders1)
	   val hyps3 = if s1 mem hyps1 then hyps2 else hyps2\s1
       in (shyps2, hyps3, max[maxidx1,maxidx2], 
	   Logic.mk_implies(s1,u1), ders2) 
       end

 in try_botc end;


(*** Meta-rewriting: rewrites t to u and returns the theorem t==u ***)
(* Parameters:
   mode = (simplify A, use A in simplifying B) when simplifying A ==> B
   mss: contains equality theorems of the form [|p1,...|] ==> t==u
   prover: how to solve premises in conditional rewrites and congruences
*)
(*** FIXME: check that #bounds(mss) does not "occur" in ct alread ***)
fun rewrite_cterm mode mss prover ct =
  let val {sign, t, T, maxidx} = rep_cterm ct;
      val (shyps,hyps,maxidxu,u,ders) =
        bottomc (mode,prover,sign) mss 
	        (add_term_sorts(t,[]), [], maxidx, t, []);
      val prop = Logic.mk_equals(t,u)
  in
      Thm{sign = sign, 
	  der = infer_derivs (Rewrite_cterm ct, ders),
	  maxidx = max[maxidx,maxidxu],
	  shyps = shyps, 
	  hyps = hyps, 
          prop = prop}
  end


fun invoke_oracle (thy, sign, exn) =
    case #oraopt(rep_theory thy) of
	None => raise THM ("No oracle in supplied theory", 0, [])
      | Some oracle => 
	    let val sign' = Sign.merge(sign_of thy, sign)
		val (prop, T, maxidx) = 
		    Sign.certify_term sign' (oracle (sign', exn))
            in if T<>propT then
                  raise THM("Oracle's result must have type prop", 0, [])
	       else fix_shyps [] []
		     (Thm {sign = sign', 
			   der = Oracle(thy,sign,exn),
			   maxidx = maxidx,
			   shyps = [], 
			   hyps = [], 
			   prop = prop})
            end;

end;

open Thm;