(*  Title:      Pure/logic.ML
    Author:     Lawrence C Paulson, Cambridge University Computer Laboratory
    Author:     Makarius

Abstract syntax operations of the Pure meta-logic.
*)

signature LOGIC =
sig
  val all_const: typ -> term
  val all: term -> term -> term
  val dependent_all_name: string * term -> term -> term
  val is_all: term -> bool
  val dest_all: term -> (string * typ) * term
  val list_all: (string * typ) list * term -> term
  val all_constraint: (string -> typ option) -> string * string -> term -> term
  val dependent_all_constraint: (string -> typ option) -> string * string -> term -> term
  val mk_equals: term * term -> term
  val dest_equals: term -> term * term
  val implies: term
  val mk_implies: term * term -> term
  val dest_implies: term -> term * term
  val list_implies: term list * term -> term
  val strip_imp_prems: term -> term list
  val strip_imp_concl: term -> term
  val strip_prems: int * term list * term -> term list * term
  val count_prems: term -> int
  val nth_prem: int * term -> term
  val close_term: (string * term) list -> term -> term
  val close_prop: (string * term) list -> term list -> term -> term
  val close_prop_constraint: (string -> typ option) ->
    (string * string) list -> term list -> term -> term
  val true_prop: term
  val conjunction: term
  val mk_conjunction: term * term -> term
  val mk_conjunction_list: term list -> term
  val mk_conjunction_balanced: term list -> term
  val dest_conjunction: term -> term * term
  val dest_conjunction_list: term -> term list
  val dest_conjunction_balanced: int -> term -> term list
  val dest_conjunctions: term -> term list
  val strip_horn: term -> term list * term
  val mk_type: typ -> term
  val dest_type: term -> typ
  val type_map: (term -> term) -> typ -> typ
  val const_of_class: class -> string
  val class_of_const: string -> class
  val mk_of_class: typ * class -> term
  val dest_of_class: term -> typ * class
  val mk_of_sort: typ * sort -> term list
  val name_classrel: string * string -> string
  val mk_classrel: class * class -> term
  val dest_classrel: term -> class * class
  val name_arities: arity -> string list
  val name_arity: string * sort list * class -> string
  val mk_arities: arity -> term list
  val mk_arity: string * sort list * class -> term
  val dest_arity: term -> string * sort list * class
  val dummy_tfree: sort -> typ
  type unconstrain_context =
   {present_map: (typ * typ) list,
    constraints_map: (sort * typ) list,
    atyp_map: typ -> typ,
    map_atyps: typ -> typ,
    constraints: ((typ * class) * term) list,
    outer_constraints: (typ * class) list};
  val unconstrainT: sort list -> term -> unconstrain_context * term
  val protectC: term
  val protect: term -> term
  val unprotect: term -> term
  val mk_term: term -> term
  val dest_term: term -> term
  val occs: term * term -> bool
  val close_form: term -> term
  val combound: term * int * int -> term
  val rlist_abs: (string * typ) list * term -> term
  val incr_tvar_same: int -> typ Same.operation
  val incr_tvar: int -> typ -> typ
  val incr_indexes_same: string list * typ list * int -> term Same.operation
  val incr_indexes: string list * typ list * int -> term -> term
  val lift_abs: int -> term -> term -> term
  val lift_all: int -> term -> term -> term
  val strip_assums_hyp: term -> term list
  val strip_assums_concl: term -> term
  val strip_params: term -> (string * typ) list
  val has_meta_prems: term -> bool
  val flatten_params: int -> term -> term
  val list_rename_params: string list -> term -> term
  val assum_pairs: int * term -> (term * term) list
  val assum_problems: int * term -> (term -> term) * term list * term
  val bad_schematic: indexname -> string
  val bad_fixed: string -> string
  val varifyT_global: typ -> typ
  val unvarifyT_global: typ -> typ
  val varify_types_global: term -> term
  val unvarify_types_global: term -> term
  val varify_global: term -> term
  val unvarify_global: term -> term
  val get_goal: term -> int -> term
  val goal_params: term -> int -> term * term list
  val prems_of_goal: term -> int -> term list
  val concl_of_goal: term -> int -> term
end;

structure Logic : LOGIC =
struct


(*** Abstract syntax operations on the meta-connectives ***)

(** all **)

fun all_const T = Const ("Pure.all", (T --> propT) --> propT);

fun all v t = all_const (Term.fastype_of v) $ lambda v t;

fun dependent_all_name (x, v) t =
  let
    val x' = if x = "" then Term.term_name v else x;
    val T = Term.fastype_of v;
    val t' = Term.abstract_over (v, t);
  in if Term.is_dependent t' then all_const T $ Abs (x', T, t') else t end;

fun is_all (Const ("Pure.all", _) $ Abs _) = true
  | is_all _ = false;

fun dest_all (Const ("Pure.all", _) $ Abs (abs as (_, T, _))) =
      let val (x, b) = Term.dest_abs abs  (*potentially slow*)
      in ((x, T), b) end
  | dest_all t = raise TERM ("dest_all", [t]);

fun list_all ([], t) = t
  | list_all ((a, T) :: vars, t) = all_const T $ Abs (a, T, list_all (vars, t));


(* operations before type-inference *)

local

fun abs_body default_type z tm =
  let
    fun abs lev (Abs (x, T, b)) = Abs (x, T, abs (lev + 1) b)
      | abs lev (t $ u) = abs lev t $ abs lev u
      | abs lev (a as Free (x, T)) =
          if x = z then
            Type.constraint (the_default dummyT (default_type x))
              (Type.constraint T (Bound lev))
          else a
      | abs _ a = a;
  in abs 0 (Term.incr_boundvars 1 tm) end;

in

fun all_constraint default_type (y, z) t =
  all_const dummyT $ Abs (y, dummyT, abs_body default_type z t);

fun dependent_all_constraint default_type (y, z) t =
  let val t' = abs_body default_type z t
  in if Term.is_dependent t' then all_const dummyT $ Abs (y, dummyT, t') else t end;

end;


(** equality **)

fun mk_equals (t, u) =
  let val T = Term.fastype_of t
  in Const ("Pure.eq", T --> T --> propT) $ t $ u end;

fun dest_equals (Const ("Pure.eq", _) $ t $ u) = (t, u)
  | dest_equals t = raise TERM ("dest_equals", [t]);



(** implies **)

val implies = Const ("Pure.imp", propT --> propT --> propT);

fun mk_implies (A, B) = implies $ A $ B;

fun dest_implies (Const ("Pure.imp", _) $ A $ B) = (A, B)
  | dest_implies A = raise TERM ("dest_implies", [A]);


(** nested implications **)

(* [A1,...,An], B  goes to  A1\<Longrightarrow>...An\<Longrightarrow>B  *)
fun list_implies ([], B) = B
  | list_implies (A::As, B) = implies $ A $ list_implies(As,B);

(* A1\<Longrightarrow>...An\<Longrightarrow>B  goes to  [A1,...,An], where B is not an implication *)
fun strip_imp_prems (Const("Pure.imp", _) $ A $ B) = A :: strip_imp_prems B
  | strip_imp_prems _ = [];

(* A1\<Longrightarrow>...An\<Longrightarrow>B  goes to B, where B is not an implication *)
fun strip_imp_concl (Const("Pure.imp", _) $ A $ B) = strip_imp_concl B
  | strip_imp_concl A = A : term;

(*Strip and return premises: (i, [], A1\<Longrightarrow>...Ai\<Longrightarrow>B)
    goes to   ([Ai, A(i-1),...,A1] , B)         (REVERSED)
  if  i<0 or else i too big then raises  TERM*)
fun strip_prems (0, As, B) = (As, B)
  | strip_prems (i, As, Const("Pure.imp", _) $ A $ B) =
        strip_prems (i-1, A::As, B)
  | strip_prems (_, As, A) = raise TERM("strip_prems", A::As);

(*Count premises -- quicker than (length o strip_prems) *)
fun count_prems (Const ("Pure.imp", _) $ _ $ B) = 1 + count_prems B
  | count_prems _ = 0;

(*Select Ai from A1\<Longrightarrow>...Ai\<Longrightarrow>B*)
fun nth_prem (1, Const ("Pure.imp", _) $ A $ _) = A
  | nth_prem (i, Const ("Pure.imp", _) $ _ $ B) = nth_prem (i - 1, B)
  | nth_prem (_, A) = raise TERM ("nth_prem", [A]);

(*strip a proof state (Horn clause):
  B1 \<Longrightarrow> ... Bn \<Longrightarrow> C   goes to   ([B1, ..., Bn], C) *)
fun strip_horn A = (strip_imp_prems A, strip_imp_concl A);


(* close -- omit vacuous quantifiers *)

val close_term = fold_rev Term.dependent_lambda_name;

fun close_prop xs As B =
  fold_rev dependent_all_name xs (list_implies (As, B));

fun close_prop_constraint default_type xs As B =
  fold_rev (dependent_all_constraint default_type) xs (list_implies (As, B));


(** conjunction **)

val true_prop = all_const propT $ Abs ("dummy", propT, mk_implies (Bound 0, Bound 0));
val conjunction = Const ("Pure.conjunction", propT --> propT --> propT);


(*A &&& B*)
fun mk_conjunction (A, B) = conjunction $ A $ B;

(*A &&& B &&& C -- improper*)
fun mk_conjunction_list [] = true_prop
  | mk_conjunction_list ts = foldr1 mk_conjunction ts;

(*(A &&& B) &&& (C &&& D) -- balanced*)
fun mk_conjunction_balanced [] = true_prop
  | mk_conjunction_balanced ts = Balanced_Tree.make mk_conjunction ts;


(*A &&& B*)
fun dest_conjunction (Const ("Pure.conjunction", _) $ A $ B) = (A, B)
  | dest_conjunction t = raise TERM ("dest_conjunction", [t]);

(*A &&& B &&& C -- improper*)
fun dest_conjunction_list t =
  (case try dest_conjunction t of
    NONE => [t]
  | SOME (A, B) => A :: dest_conjunction_list B);

(*(A &&& B) &&& (C &&& D) -- balanced*)
fun dest_conjunction_balanced 0 _ = []
  | dest_conjunction_balanced n t = Balanced_Tree.dest dest_conjunction n t;

(*((A &&& B) &&& C) &&& D &&& E -- flat*)
fun dest_conjunctions t =
  (case try dest_conjunction t of
    NONE => [t]
  | SOME (A, B) => dest_conjunctions A @ dest_conjunctions B);



(** types as terms **)

fun mk_type ty = Const ("Pure.type", Term.itselfT ty);

fun dest_type (Const ("Pure.type", Type ("itself", [ty]))) = ty
  | dest_type t = raise TERM ("dest_type", [t]);

fun type_map f = dest_type o f o mk_type;



(** type classes **)

(* const names *)

val classN = "_class";

val const_of_class = suffix classN;

fun class_of_const c = unsuffix classN c
  handle Fail _ => raise TERM ("class_of_const: bad name " ^ quote c, []);


(* class/sort membership *)

fun mk_of_class (ty, c) =
  Const (const_of_class c, Term.itselfT ty --> propT) $ mk_type ty;

fun dest_of_class (Const (c_class, _) $ ty) = (dest_type ty, class_of_const c_class)
  | dest_of_class t = raise TERM ("dest_of_class", [t]);

fun mk_of_sort (ty, S) = map (fn c => mk_of_class (ty, c)) S;


(* class relations *)

fun name_classrel (c1, c2) =
  Long_Name.base_name c1 ^ "_" ^ Long_Name.base_name c2;

fun mk_classrel (c1, c2) = mk_of_class (Term.aT [c1], c2);

fun dest_classrel tm =
  (case dest_of_class tm of
    (TVar (_, [c1]), c2) => (c1, c2)
  | _ => raise TERM ("dest_classrel", [tm]));


(* type arities *)

fun name_arities (t, _, S) =
  let val b = Long_Name.base_name t
  in S |> map (fn c => Long_Name.base_name c ^ "_" ^ b) end;

fun name_arity (t, dom, c) = hd (name_arities (t, dom, [c]));

fun mk_arities (t, Ss, S) =
  let val T = Type (t, ListPair.map TFree (Name.invent Name.context Name.aT (length Ss), Ss))
  in map (fn c => mk_of_class (T, c)) S end;

fun mk_arity (t, Ss, c) = the_single (mk_arities (t, Ss, [c]));

fun dest_arity tm =
  let
    fun err () = raise TERM ("dest_arity", [tm]);

    val (ty, c) = dest_of_class tm;
    val (t, tvars) =
      (case ty of
        Type (t, tys) => (t, map dest_TVar tys handle TYPE _ => err ())
      | _ => err ());
    val Ss =
      if has_duplicates (eq_fst (op =)) tvars then err ()
      else map snd tvars;
  in (t, Ss, c) end;


(* internalized sort constraints *)

fun dummy_tfree S = TFree ("'dummy", S);

type unconstrain_context =
 {present_map: (typ * typ) list,
  constraints_map: (sort * typ) list,
  atyp_map: typ -> typ,
  map_atyps: typ -> typ,
  constraints: ((typ * class) * term) list,
  outer_constraints: (typ * class) list};

fun unconstrainT shyps prop =
  let
    val present = rev ((fold_types o fold_atyps_sorts) (insert (eq_fst op =)) prop []);
    val extra = fold (Sorts.remove_sort o #2) present shyps;

    val n = length present;
    val (names1, names2) = Name.invent Name.context Name.aT (n + length extra) |> chop n;

    val present_map =
      map2 (fn (T, S) => fn a => (T, TVar ((a, 0), S))) present names1;
    val constraints_map =
      map2 (fn (_, S) => fn a => (S, TVar ((a, 0), S))) present names1 @
      map2 (fn S => fn a => (S, TVar ((a, 0), S))) extra names2;

    fun atyp_map T =
      (case AList.lookup (op =) present_map T of
        SOME U => U
      | NONE =>
          (case AList.lookup (op =) constraints_map (Type.sort_of_atyp T) of
            SOME U => U
          | NONE => raise TYPE ("Dangling type variable ", [T], [prop])));

    val map_atyps = Term.map_atyps (Type.strip_sorts o atyp_map);

    val constraints =
      constraints_map |> maps (fn (_, T as TVar (ai, S)) =>
        map (fn c => ((T, c), mk_of_class (TVar (ai, []), c))) S);

    val outer_constraints =
      maps (fn (T, S) => map (pair T) S) (present @ map (`dummy_tfree) extra);

    val ucontext =
     {present_map = present_map,
      constraints_map = constraints_map,
      atyp_map = atyp_map,
      map_atyps = map_atyps,
      constraints = constraints,
      outer_constraints = outer_constraints};
    val prop' = prop
      |> Term.map_types map_atyps
      |> curry list_implies (map #2 constraints);
  in (ucontext, prop') end;



(** protected propositions and embedded terms **)

val protectC = Const ("Pure.prop", propT --> propT);
fun protect t = protectC $ t;

fun unprotect (Const ("Pure.prop", _) $ t) = t
  | unprotect t = raise TERM ("unprotect", [t]);


fun mk_term t = Const ("Pure.term", Term.fastype_of t --> propT) $ t;

fun dest_term (Const ("Pure.term", _) $ t) = t
  | dest_term t = raise TERM ("dest_term", [t]);



(*** Low-level term operations ***)

(*Does t occur in u?  Or is alpha-convertible to u?
  The term t must contain no loose bound variables*)
fun occs (t, u) = exists_subterm (fn s => t aconv s) u;

(*Close up a formula over all free variables by quantification*)
fun close_form A = fold (all o Free) (Term.add_frees A []) A;



(*** Specialized operations for resolution... ***)

(*computes t(Bound(n+k-1),...,Bound(n))  *)
fun combound (t, n, k) =
    if  k>0  then  combound (t,n+1,k-1) $ (Bound n)  else  t;

(* ([xn,...,x1], t)   goes to   \<lambda>x1 ... xn. t *)
fun rlist_abs ([], body) = body
  | rlist_abs ((a,T)::pairs, body) = rlist_abs(pairs, Abs(a, T, body));

fun incr_tvar_same 0 = Same.same
  | incr_tvar_same k = Term_Subst.map_atypsT_same
      (fn TVar ((a, i), S) => TVar ((a, i + k), S)
        | _ => raise Same.SAME);

fun incr_tvar k T = incr_tvar_same k T handle Same.SAME => T;

(*For all variables in the term, increment indexnames and lift over the Us
    result is ?Gidx(B.(lev+n-1),...,B.lev) where lev is abstraction level *)
fun incr_indexes_same ([], [], 0) = Same.same
  | incr_indexes_same (fixed, Ts, k) =
      let
        val n = length Ts;
        val incrT = incr_tvar_same k;

        fun incr lev (Var ((x, i), T)) =
              combound (Var ((x, i + k), Ts ---> Same.commit incrT T), lev, n)
          | incr lev (Free (x, T)) =
              if member (op =) fixed x then
                combound (Free (x, Ts ---> Same.commit incrT T), lev, n)
              else Free (x, incrT T)
          | incr lev (Abs (x, T, body)) =
              (Abs (x, incrT T, incr (lev + 1) body handle Same.SAME => body)
                handle Same.SAME => Abs (x, T, incr (lev + 1) body))
          | incr lev (t $ u) =
              (incr lev t $ (incr lev u handle Same.SAME => u)
                handle Same.SAME => t $ incr lev u)
          | incr _ (Const (c, T)) = Const (c, incrT T)
          | incr _ (Bound _) = raise Same.SAME;
      in incr 0 end;

fun incr_indexes arg t = incr_indexes_same arg t handle Same.SAME => t;


(* Lifting functions from subgoal and increment:
    lift_abs operates on terms
    lift_all operates on propositions *)

fun lift_abs inc =
  let
    fun lift Ts (Const ("Pure.imp", _) $ _ $ B) t = lift Ts B t
      | lift Ts (Const ("Pure.all", _) $ Abs (a, T, B)) t = Abs (a, T, lift (T :: Ts) B t)
      | lift Ts _ t = incr_indexes ([], rev Ts, inc) t;
  in lift [] end;

fun lift_all inc =
  let
    fun lift Ts ((c as Const ("Pure.imp", _)) $ A $ B) t = c $ A $ lift Ts B t
      | lift Ts ((c as Const ("Pure.all", _)) $ Abs (a, T, B)) t = c $ Abs (a, T, lift (T :: Ts) B t)
      | lift Ts _ t = incr_indexes ([], rev Ts, inc) t;
  in lift [] end;

(*Strips assumptions in goal, yielding list of hypotheses.   *)
fun strip_assums_hyp B =
  let
    fun strip Hs (Const ("Pure.imp", _) $ H $ B) = strip (H :: Hs) B
      | strip Hs (Const ("Pure.all", _) $ Abs (a, T, t)) =
          strip (map (incr_boundvars 1) Hs) t
      | strip Hs B = rev Hs
  in strip [] B end;

(*Strips assumptions in goal, yielding conclusion.   *)
fun strip_assums_concl (Const("Pure.imp", _) $ H $ B) = strip_assums_concl B
  | strip_assums_concl (Const("Pure.all", _) $ Abs (a, T, t)) = strip_assums_concl t
  | strip_assums_concl B = B;

(*Make a list of all the parameters in a subgoal, even if nested*)
fun strip_params (Const("Pure.imp", _) $ H $ B) = strip_params B
  | strip_params (Const("Pure.all", _) $ Abs (a, T, t)) = (a, T) :: strip_params t
  | strip_params B = [];

(*test for nested meta connectives in prems*)
val has_meta_prems =
  let
    fun is_meta (Const ("Pure.eq", _) $ _ $ _) = true
      | is_meta (Const ("Pure.imp", _) $ _ $ _) = true
      | is_meta (Const ("Pure.all", _) $ _) = true
      | is_meta _ = false;
    fun ex_meta (Const ("Pure.imp", _) $ A $ B) = is_meta A orelse ex_meta B
      | ex_meta (Const ("Pure.all", _) $ Abs (_, _, B)) = ex_meta B
      | ex_meta _ = false;
  in ex_meta end;

(*Removes the parameters from a subgoal and renumber bvars in hypotheses,
    where j is the total number of parameters (precomputed)
  If n>0 then deletes assumption n. *)
fun remove_params j n A =
    if j=0 andalso n<=0 then A  (*nothing left to do...*)
    else case A of
        Const("Pure.imp", _) $ H $ B =>
          if n=1 then                           (remove_params j (n-1) B)
          else implies $ (incr_boundvars j H) $ (remove_params j (n-1) B)
      | Const("Pure.all",_)$Abs(a,T,t) => remove_params (j-1) n t
      | _ => if n>0 then raise TERM("remove_params", [A])
             else A;

(*Move all parameters to the front of the subgoal, renaming them apart;
  if n>0 then deletes assumption n. *)
fun flatten_params n A =
    let val params = strip_params A;
        val vars = ListPair.zip (Name.variant_list [] (map #1 params),
                                 map #2 params)
    in list_all (vars, remove_params (length vars) n A) end;

(*Makes parameters in a goal have the names supplied by the list cs.*)
fun list_rename_params cs (Const ("Pure.imp", _) $ A $ B) =
      implies $ A $ list_rename_params cs B
  | list_rename_params (c :: cs) ((a as Const ("Pure.all", _)) $ Abs (_, T, t)) =
      a $ Abs (c, T, list_rename_params cs t)
  | list_rename_params cs B = B;



(*** Treatment of "assume", "erule", etc. ***)

(*Strips assumptions in goal yielding
   HS = [Hn,...,H1],   params = [xm,...,x1], and B,
  where x1...xm are the parameters. This version (21.1.2005) REQUIRES
  the the parameters to be flattened, but it allows erule to work on
  assumptions of the form \<And>x. phi. Any \<And> after the outermost string
  will be regarded as belonging to the conclusion, and left untouched.
  Used ONLY by assum_pairs.
      Unless nasms<0, it can terminate the recursion early; that allows
  erule to work on assumptions of the form P\<Longrightarrow>Q.*)
fun strip_assums_imp (0, Hs, B) = (Hs, B)  (*recursion terminated by nasms*)
  | strip_assums_imp (nasms, Hs, Const("Pure.imp", _) $ H $ B) =
      strip_assums_imp (nasms-1, H::Hs, B)
  | strip_assums_imp (_, Hs, B) = (Hs, B); (*recursion terminated by B*)

(*Strips OUTER parameters only.*)
fun strip_assums_all (params, Const("Pure.all",_)$Abs(a,T,t)) =
      strip_assums_all ((a,T)::params, t)
  | strip_assums_all (params, B) = (params, B);

(*Produces disagreement pairs, one for each assumption proof, in order.
  A is the first premise of the lifted rule, and thus has the form
    H1 \<Longrightarrow> ... Hk \<Longrightarrow> B   and the pairs are (H1,B),...,(Hk,B).
  nasms is the number of assumptions in the original subgoal, needed when B
    has the form B1 \<Longrightarrow> B2: it stops B1 from being taken as an assumption. *)
fun assum_pairs(nasms,A) =
  let val (params, A') = strip_assums_all ([],A)
      val (Hs,B) = strip_assums_imp (nasms,[],A')
      fun abspar t = rlist_abs(params, t)
      val D = abspar B
      fun pairrev ([], pairs) = pairs
        | pairrev (H::Hs, pairs) = pairrev(Hs,  (abspar H, D) :: pairs)
  in  pairrev (Hs,[])
  end;

fun assum_problems (nasms, A) =
  let
    val (params, A') = strip_assums_all ([], A)
    val (Hs, B) = strip_assums_imp (nasms, [], A')
    fun abspar t = rlist_abs (params, t)
  in (abspar, rev Hs, B) end;


(* global schematic variables *)

fun bad_schematic xi = "Illegal schematic variable: " ^ quote (Term.string_of_vname xi);
fun bad_fixed x = "Illegal fixed variable: " ^ quote x;

fun varifyT_global_same ty = ty
  |> Term_Subst.map_atypsT_same
    (fn TFree (a, S) => TVar ((a, 0), S)
      | TVar (ai, _) => raise TYPE (bad_schematic ai, [ty], []));

fun unvarifyT_global_same ty = ty
  |> Term_Subst.map_atypsT_same
    (fn TVar ((a, 0), S) => TFree (a, S)
      | TVar (ai, _) => raise TYPE (bad_schematic ai, [ty], [])
      | TFree (a, _) => raise TYPE (bad_fixed a, [ty], []));

val varifyT_global = Same.commit varifyT_global_same;
val unvarifyT_global = Same.commit unvarifyT_global_same;

fun varify_types_global tm = tm
  |> Same.commit (Term_Subst.map_types_same varifyT_global_same)
  handle TYPE (msg, _, _) => raise TERM (msg, [tm]);

fun unvarify_types_global tm = tm
  |> Same.commit (Term_Subst.map_types_same unvarifyT_global_same)
  handle TYPE (msg, _, _) => raise TERM (msg, [tm]);

fun varify_global tm = tm
  |> Same.commit (Term_Subst.map_aterms_same
    (fn Free (x, T) => Var ((x, 0), T)
      | Var (xi, _) => raise TERM (bad_schematic xi, [tm])
      | _ => raise Same.SAME))
  |> varify_types_global;

fun unvarify_global tm = tm
  |> Same.commit (Term_Subst.map_aterms_same
    (fn Var ((x, 0), T) => Free (x, T)
      | Var (xi, _) => raise TERM (bad_schematic xi, [tm])
      | Free (x, _) => raise TERM (bad_fixed x, [tm])
      | _ => raise Same.SAME))
  |> unvarify_types_global;


(* goal states *)

fun get_goal st i =
  nth_prem (i, st) handle TERM _ =>
    error ("Subgoal number " ^ string_of_int i ^ " out of range (a total of " ^
      string_of_int (count_prems st)  ^ " subgoals)");

(*reverses parameters for substitution*)
fun goal_params st i =
  let val gi = get_goal st i
      val rfrees = map Free (Term.rename_wrt_term gi (strip_params gi))
  in (gi, rfrees) end;

fun concl_of_goal st i =
  let val (gi, rfrees) = goal_params st i
      val B = strip_assums_concl gi
  in subst_bounds (rfrees, B) end;

fun prems_of_goal st i =
  let val (gi, rfrees) = goal_params st i
      val As = strip_assums_hyp gi
  in map (fn A => subst_bounds (rfrees, A)) As end;

end;