src/HOL/Tools/ATP/atp_reconstruct.ML

made SML/NJ happy

(*  Title:      HOL/Tools/ATP/atp_reconstruct.ML
    Author:     Lawrence C. Paulson, Cambridge University Computer Laboratory
    Author:     Claire Quigley, Cambridge University Computer Laboratory
    Author:     Jasmin Blanchette, TU Muenchen

Proof reconstruction from ATP proofs.
*)

signature ATP_RECONSTRUCT =
sig
  type ('a, 'b) ho_term = ('a, 'b) ATP_Problem.ho_term
  type ('a, 'b, 'c) formula = ('a, 'b, 'c) ATP_Problem.formula
  type step_name = ATP_Proof.step_name
  type 'a proof = 'a ATP_Proof.proof
  type locality = ATP_Translate.locality

  datatype reconstructor =
    Metis of string * string |
    SMT

  datatype play =
    Played of reconstructor * Time.time |
    Trust_Playable of reconstructor * Time.time option |
    Failed_to_Play of reconstructor

  type minimize_command = string list -> string
  type one_line_params =
    play * string * (string * locality) list * minimize_command * int * int
  type isar_params =
    bool * int * string Symtab.table * (string * locality) list vector
    * int Symtab.table * string proof * thm

  val metisN : string
  val smtN : string
  val full_typesN : string
  val partial_typesN : string
  val no_typesN : string
  val really_full_type_enc : string
  val full_type_enc : string
  val partial_type_enc : string
  val no_type_enc : string
  val full_type_encs : string list
  val partial_type_encs : string list
  val metis_default_lam_trans : string
  val metis_call : string -> string -> string
  val string_for_reconstructor : reconstructor -> string
  val used_facts_in_atp_proof :
    Proof.context -> (string * locality) list vector -> string proof
    -> (string * locality) list
  val lam_trans_from_atp_proof : string proof -> string -> string
  val is_typed_helper_used_in_atp_proof : string proof -> bool
  val used_facts_in_unsound_atp_proof :
    Proof.context -> (string * locality) list vector -> 'a proof
    -> string list option
  val unalias_type_enc : string -> string list
  val one_line_proof_text : one_line_params -> string
  val make_tvar : string -> typ
  val make_tfree : Proof.context -> string -> typ
  val term_from_atp :
    Proof.context -> bool -> int Symtab.table -> typ option
    -> (string, string) ho_term -> term
  val prop_from_atp :
    Proof.context -> bool -> int Symtab.table
    -> (string, string, (string, string) ho_term) formula -> term
  val isar_proof_text :
    Proof.context -> bool -> isar_params -> one_line_params -> string
  val proof_text :
    Proof.context -> bool -> isar_params -> one_line_params -> string
end;

structure ATP_Reconstruct : ATP_RECONSTRUCT =
struct

open ATP_Util
open ATP_Problem
open ATP_Proof
open ATP_Translate

datatype reconstructor =
  Metis of string * string |
  SMT

datatype play =
  Played of reconstructor * Time.time |
  Trust_Playable of reconstructor * Time.time option |
  Failed_to_Play of reconstructor

type minimize_command = string list -> string
type one_line_params =
  play * string * (string * locality) list * minimize_command * int * int
type isar_params =
  bool * int * string Symtab.table * (string * locality) list vector
  * int Symtab.table * string proof * thm

val metisN = "metis"
val smtN = "smt"

val full_typesN = "full_types"
val partial_typesN = "partial_types"
val no_typesN = "no_types"

val really_full_type_enc = "mono_tags"
val full_type_enc = "poly_guards_query"
val partial_type_enc = "poly_args"
val no_type_enc = "erased"

val full_type_encs = [full_type_enc, really_full_type_enc]
val partial_type_encs = partial_type_enc :: full_type_encs

val type_enc_aliases =
  [(full_typesN, full_type_encs),
   (partial_typesN, partial_type_encs),
   (no_typesN, [no_type_enc])]

fun unalias_type_enc s =
  AList.lookup (op =) type_enc_aliases s |> the_default [s]

val metis_default_lam_trans = combinatorsN

fun metis_call type_enc lam_trans =
  let
    val type_enc =
      case AList.find (fn (enc, encs) => enc = hd encs) type_enc_aliases
                      type_enc of
        [alias] => alias
      | _ => type_enc
    val opts = [] |> type_enc <> partial_typesN ? cons type_enc
                  |> lam_trans <> metis_default_lam_trans ? cons lam_trans
  in metisN ^ (if null opts then "" else " (" ^ commas opts ^ ")") end

fun string_for_reconstructor (Metis (type_enc, lam_trans)) =
    metis_call type_enc lam_trans
  | string_for_reconstructor SMT = smtN

fun find_first_in_list_vector vec key =
  Vector.foldl (fn (ps, NONE) => AList.lookup (op =) ps key
                 | (_, value) => value) NONE vec

val unprefix_fact_number = space_implode "_" o tl o space_explode "_"

fun resolve_one_named_fact fact_names s =
  case try (unprefix fact_prefix) s of
    SOME s' =>
    let val s' = s' |> unprefix_fact_number |> unascii_of in
      s' |> find_first_in_list_vector fact_names |> Option.map (pair s')
    end
  | NONE => NONE
fun resolve_fact fact_names = map_filter (resolve_one_named_fact fact_names)
fun is_fact fact_names = not o null o resolve_fact fact_names

fun resolve_one_named_conjecture s =
  case try (unprefix conjecture_prefix) s of
    SOME s' => Int.fromString s'
  | NONE => NONE

val resolve_conjecture = map_filter resolve_one_named_conjecture
val is_conjecture = not o null o resolve_conjecture

fun is_axiom_used_in_proof pred =
  exists (fn Inference ((_, ss), _, _, []) => exists pred ss | _ => false)

val is_combinator_def = String.isPrefix (helper_prefix ^ combinator_prefix)

val ascii_of_lam_fact_prefix = ascii_of lam_fact_prefix

(* overapproximation (good enough) *)
fun is_lam_lifted s =
  String.isPrefix fact_prefix s andalso
  String.isSubstring ascii_of_lam_fact_prefix s

fun lam_trans_from_atp_proof atp_proof default =
  if is_axiom_used_in_proof is_combinator_def atp_proof then combinatorsN
  else if is_axiom_used_in_proof is_lam_lifted atp_proof then lam_liftingN
  else default

val is_typed_helper_name =
  String.isPrefix helper_prefix andf String.isSuffix typed_helper_suffix
fun is_typed_helper_used_in_atp_proof atp_proof =
  is_axiom_used_in_proof is_typed_helper_name atp_proof

val leo2_ext = "extcnf_equal_neg"
val isa_ext = Thm.get_name_hint @{thm ext}
val isa_short_ext = Long_Name.base_name isa_ext

fun ext_name ctxt =
  if Thm.eq_thm_prop (@{thm ext},
         singleton (Attrib.eval_thms ctxt) (Facts.named isa_short_ext, [])) then
    isa_short_ext
  else
    isa_ext

fun add_fact _ fact_names (Inference ((_, ss), _, _, [])) =
    union (op =) (resolve_fact fact_names ss)
  | add_fact ctxt _ (Inference (_, _, rule, _)) =
    if rule = leo2_ext then insert (op =) (ext_name ctxt, General) else I
  | add_fact _ _ _ = I

fun used_facts_in_atp_proof ctxt fact_names atp_proof =
  if null atp_proof then Vector.foldl (uncurry (union (op =))) [] fact_names
  else fold (add_fact ctxt fact_names) atp_proof []

(* (quasi-)underapproximation of the truth *)
fun is_locality_global Local = false
  | is_locality_global Assum = false
  | is_locality_global Chained = false
  | is_locality_global _ = true

fun used_facts_in_unsound_atp_proof _ _ [] = NONE
  | used_facts_in_unsound_atp_proof ctxt fact_names atp_proof =
    let
      val used_facts = used_facts_in_atp_proof ctxt fact_names atp_proof
    in
      if forall (is_locality_global o snd) used_facts andalso
         not (is_axiom_used_in_proof (is_conjecture o single) atp_proof) then
        SOME (map fst used_facts)
      else
        NONE
    end


(** Soft-core proof reconstruction: one-liners **)

fun string_for_label (s, num) = s ^ string_of_int num

fun show_time NONE = ""
  | show_time (SOME ext_time) = " (" ^ string_from_ext_time ext_time ^ ")"

fun apply_on_subgoal _ 1 = "by "
  | apply_on_subgoal 1 _ = "apply "
  | apply_on_subgoal i n =
    "prefer " ^ string_of_int i ^ " " ^ apply_on_subgoal 1 n
fun command_call name [] =
    name |> not (Lexicon.is_identifier name) ? enclose "(" ")"
  | command_call name args = "(" ^ name ^ " " ^ space_implode " " args ^ ")"
fun try_command_line banner time command =
  banner ^ ": " ^ Markup.markup Markup.sendback command ^ show_time time ^ "."
fun using_labels [] = ""
  | using_labels ls =
    "using " ^ space_implode " " (map string_for_label ls) ^ " "
fun reconstructor_command reconstr i n (ls, ss) =
  using_labels ls ^ apply_on_subgoal i n ^
  command_call (string_for_reconstructor reconstr) ss
fun minimize_line _ [] = ""
  | minimize_line minimize_command ss =
    case minimize_command ss of
      "" => ""
    | command => "\nTo minimize: " ^ Markup.markup Markup.sendback command ^ "."

val split_used_facts =
  List.partition (curry (op =) Chained o snd)
  #> pairself (sort_distinct (string_ord o pairself fst))

fun one_line_proof_text (preplay, banner, used_facts, minimize_command,
                         subgoal, subgoal_count) =
  let
    val (chained, extra) = split_used_facts used_facts
    val (failed, reconstr, ext_time) =
      case preplay of
        Played (reconstr, time) => (false, reconstr, (SOME (false, time)))
      | Trust_Playable (reconstr, time) =>
        (false, reconstr,
         case time of
           NONE => NONE
         | SOME time =>
           if time = Time.zeroTime then NONE else SOME (true, time))
      | Failed_to_Play reconstr => (true, reconstr, NONE)
    val try_line =
      ([], map fst extra)
      |> reconstructor_command reconstr subgoal subgoal_count
      |> (if failed then enclose "One-line proof reconstruction failed: " "."
          else try_command_line banner ext_time)
  in try_line ^ minimize_line minimize_command (map fst (extra @ chained)) end

(** Hard-core proof reconstruction: structured Isar proofs **)

fun forall_of v t = HOLogic.all_const (fastype_of v) $ lambda v t
fun exists_of v t = HOLogic.exists_const (fastype_of v) $ lambda v t

fun make_tvar s = TVar (("'" ^ s, 0), HOLogic.typeS)
fun make_tfree ctxt w =
  let val ww = "'" ^ w in
    TFree (ww, the_default HOLogic.typeS (Variable.def_sort ctxt (ww, ~1)))
  end

val indent_size = 2
val no_label = ("", ~1)

val raw_prefix = "X"
val assum_prefix = "A"
val have_prefix = "F"

fun raw_label_for_name (num, ss) =
  case resolve_conjecture ss of
    [j] => (conjecture_prefix, j)
  | _ => case Int.fromString num of
           SOME j => (raw_prefix, j)
         | NONE => (raw_prefix ^ num, 0)

(**** INTERPRETATION OF TSTP SYNTAX TREES ****)

exception HO_TERM of (string, string) ho_term list
exception FORMULA of (string, string, (string, string) ho_term) formula list
exception SAME of unit

(* Type variables are given the basic sort "HOL.type". Some will later be
   constrained by information from type literals, or by type inference. *)
fun typ_from_atp ctxt (u as ATerm (a, us)) =
  let val Ts = map (typ_from_atp ctxt) us in
    case unprefix_and_unascii type_const_prefix a of
      SOME b => Type (invert_const b, Ts)
    | NONE =>
      if not (null us) then
        raise HO_TERM [u]  (* only "tconst"s have type arguments *)
      else case unprefix_and_unascii tfree_prefix a of
        SOME b => make_tfree ctxt b
      | NONE =>
        (* Could be an Isabelle variable or a variable from the ATP, say "X1"
           or "_5018". Sometimes variables from the ATP are indistinguishable
           from Isabelle variables, which forces us to use a type parameter in
           all cases. *)
        (a |> perhaps (unprefix_and_unascii tvar_prefix), HOLogic.typeS)
        |> Type_Infer.param 0
  end

(* Type class literal applied to a type. Returns triple of polarity, class,
   type. *)
fun type_constraint_from_term ctxt (u as ATerm (a, us)) =
  case (unprefix_and_unascii class_prefix a, map (typ_from_atp ctxt) us) of
    (SOME b, [T]) => (b, T)
  | _ => raise HO_TERM [u]

(* Accumulate type constraints in a formula: negative type literals. *)
fun add_var (key, z)  = Vartab.map_default (key, []) (cons z)
fun add_type_constraint false (cl, TFree (a ,_)) = add_var ((a, ~1), cl)
  | add_type_constraint false (cl, TVar (ix, _)) = add_var (ix, cl)
  | add_type_constraint _ _ = I

fun repair_variable_name f s =
  let
    fun subscript_name s n = s ^ nat_subscript n
    val s = String.map f s
  in
    case space_explode "_" s of
      [_] => (case take_suffix Char.isDigit (String.explode s) of
                (cs1 as _ :: _, cs2 as _ :: _) =>
                subscript_name (String.implode cs1)
                               (the (Int.fromString (String.implode cs2)))
              | (_, _) => s)
    | [s1, s2] => (case Int.fromString s2 of
                     SOME n => subscript_name s1 n
                   | NONE => s)
    | _ => s
  end

(* The number of type arguments of a constant, zero if it's monomorphic. For
   (instances of) Skolem pseudoconstants, this information is encoded in the
   constant name. *)
fun num_type_args thy s =
  if String.isPrefix skolem_const_prefix s then
    s |> space_explode Long_Name.separator |> List.last |> Int.fromString |> the
  else if String.isPrefix lam_lifted_prefix s then
    if String.isPrefix lam_lifted_poly_prefix s then 2 else 0
  else
    (s, Sign.the_const_type thy s) |> Sign.const_typargs thy |> length

fun slack_fastype_of t = fastype_of t handle TERM _ => HOLogic.typeT

(* First-order translation. No types are known for variables. "HOLogic.typeT"
   should allow them to be inferred. *)
fun term_from_atp ctxt textual sym_tab =
  let
    val thy = Proof_Context.theory_of ctxt
    (* For Metis, we use 1 rather than 0 because variable references in clauses
       may otherwise conflict with variable constraints in the goal. At least,
       type inference often fails otherwise. See also "axiom_inference" in
       "Metis_Reconstruct". *)
    val var_index = if textual then 0 else 1
    fun do_term extra_ts opt_T u =
      case u of
        ATerm (s, us) =>
        if String.isPrefix simple_type_prefix s then
          @{const True} (* ignore TPTP type information *)
        else if s = tptp_equal then
          let val ts = map (do_term [] NONE) us in
            if textual andalso length ts = 2 andalso
              hd ts aconv List.last ts then
              (* Vampire is keen on producing these. *)
              @{const True}
            else
              list_comb (Const (@{const_name HOL.eq}, HOLogic.typeT), ts)
          end
        else case unprefix_and_unascii const_prefix s of
          SOME s' =>
          let
            val ((s', s''), mangled_us) =
              s' |> unmangled_const |>> `invert_const
          in
            if s' = type_tag_name then
              case mangled_us @ us of
                [typ_u, term_u] =>
                do_term extra_ts (SOME (typ_from_atp ctxt typ_u)) term_u
              | _ => raise HO_TERM us
            else if s' = predicator_name then
              do_term [] (SOME @{typ bool}) (hd us)
            else if s' = app_op_name then
              let val extra_t = do_term [] NONE (List.last us) in
                do_term (extra_t :: extra_ts)
                        (case opt_T of
                           SOME T => SOME (slack_fastype_of extra_t --> T)
                         | NONE => NONE)
                        (nth us (length us - 2))
              end
            else if s' = type_guard_name then
              @{const True} (* ignore type predicates *)
            else
              let
                val new_skolem = String.isPrefix new_skolem_const_prefix s''
                val num_ty_args =
                  length us - the_default 0 (Symtab.lookup sym_tab s)
                val (type_us, term_us) =
                  chop num_ty_args us |>> append mangled_us
                val term_ts = map (do_term [] NONE) term_us
                val T =
                  (if not (null type_us) andalso
                      num_type_args thy s' = length type_us then
                     let val Ts = type_us |> map (typ_from_atp ctxt) in
                       if new_skolem then
                         SOME (Type_Infer.paramify_vars (tl Ts ---> hd Ts))
                       else if textual then
                         try (Sign.const_instance thy) (s', Ts)
                       else
                         NONE
                     end
                   else
                     NONE)
                  |> (fn SOME T => T
                       | NONE => map slack_fastype_of term_ts --->
                                 (case opt_T of
                                    SOME T => T
                                  | NONE => HOLogic.typeT))
                val t =
                  if new_skolem then
                    Var ((new_skolem_var_name_from_const s'', var_index), T)
                  else
                    Const (unproxify_const s', T)
              in list_comb (t, term_ts @ extra_ts) end
          end
        | NONE => (* a free or schematic variable *)
          let
            val term_ts = map (do_term [] NONE) us
            val ts = term_ts @ extra_ts
            val T =
              case opt_T of
                SOME T => map slack_fastype_of term_ts ---> T
              | NONE => map slack_fastype_of ts ---> HOLogic.typeT
            val t =
              case unprefix_and_unascii fixed_var_prefix s of
                SOME s => Free (s, T)
              | NONE =>
                case unprefix_and_unascii schematic_var_prefix s of
                  SOME s => Var ((s, var_index), T)
                | NONE =>
                  Var ((s |> textual ? repair_variable_name Char.toLower,
                        var_index), T)
          in list_comb (t, ts) end
  in do_term [] end

fun term_from_atom ctxt textual sym_tab pos (u as ATerm (s, _)) =
  if String.isPrefix class_prefix s then
    add_type_constraint pos (type_constraint_from_term ctxt u)
    #> pair @{const True}
  else
    pair (term_from_atp ctxt textual sym_tab (SOME @{typ bool}) u)

val combinator_table =
  [(@{const_name Meson.COMBI}, @{thm Meson.COMBI_def_raw}),
   (@{const_name Meson.COMBK}, @{thm Meson.COMBK_def_raw}),
   (@{const_name Meson.COMBB}, @{thm Meson.COMBB_def_raw}),
   (@{const_name Meson.COMBC}, @{thm Meson.COMBC_def_raw}),
   (@{const_name Meson.COMBS}, @{thm Meson.COMBS_def_raw})]

fun uncombine_term thy =
  let
    fun aux (t1 $ t2) = betapply (pairself aux (t1, t2))
      | aux (Abs (s, T, t')) = Abs (s, T, aux t')
      | aux (t as Const (x as (s, _))) =
        (case AList.lookup (op =) combinator_table s of
           SOME thm => thm |> prop_of |> specialize_type thy x
                           |> Logic.dest_equals |> snd
         | NONE => t)
      | aux t = t
  in aux end

(* Update schematic type variables with detected sort constraints. It's not
   totally clear whether this code is necessary. *)
fun repair_tvar_sorts (t, tvar_tab) =
  let
    fun do_type (Type (a, Ts)) = Type (a, map do_type Ts)
      | do_type (TVar (xi, s)) =
        TVar (xi, the_default s (Vartab.lookup tvar_tab xi))
      | do_type (TFree z) = TFree z
    fun do_term (Const (a, T)) = Const (a, do_type T)
      | do_term (Free (a, T)) = Free (a, do_type T)
      | do_term (Var (xi, T)) = Var (xi, do_type T)
      | do_term (t as Bound _) = t
      | do_term (Abs (a, T, t)) = Abs (a, do_type T, do_term t)
      | do_term (t1 $ t2) = do_term t1 $ do_term t2
  in t |> not (Vartab.is_empty tvar_tab) ? do_term end

fun quantify_over_var quant_of var_s t =
  let
    val vars = [] |> Term.add_vars t |> filter (fn ((s, _), _) => s = var_s)
                  |> map Var
  in fold_rev quant_of vars t end

(* Interpret an ATP formula as a HOL term, extracting sort constraints as they
   appear in the formula. *)
fun prop_from_atp ctxt textual sym_tab phi =
  let
    fun do_formula pos phi =
      case phi of
        AQuant (_, [], phi) => do_formula pos phi
      | AQuant (q, (s, _) :: xs, phi') =>
        do_formula pos (AQuant (q, xs, phi'))
        (* FIXME: TFF *)
        #>> quantify_over_var (case q of
                                 AForall => forall_of
                               | AExists => exists_of)
                              (s |> textual ? repair_variable_name Char.toLower)
      | AConn (ANot, [phi']) => do_formula (not pos) phi' #>> s_not
      | AConn (c, [phi1, phi2]) =>
        do_formula (pos |> c = AImplies ? not) phi1
        ##>> do_formula pos phi2
        #>> (case c of
               AAnd => s_conj
             | AOr => s_disj
             | AImplies => s_imp
             | AIff => s_iff
             | ANot => raise Fail "impossible connective")
      | AAtom tm => term_from_atom ctxt textual sym_tab pos tm
      | _ => raise FORMULA [phi]
  in repair_tvar_sorts (do_formula true phi Vartab.empty) end

fun infer_formula_types ctxt =
  Type.constraint HOLogic.boolT
  #> Syntax.check_term
         (Proof_Context.set_mode Proof_Context.mode_schematic ctxt)

fun uncombined_etc_prop_from_atp ctxt textual sym_tab =
  let val thy = Proof_Context.theory_of ctxt in
    prop_from_atp ctxt textual sym_tab
    #> textual ? uncombine_term thy #> infer_formula_types ctxt
  end

(**** Translation of TSTP files to Isar proofs ****)

fun unvarify_term (Var ((s, 0), T)) = Free (s, T)
  | unvarify_term t = raise TERM ("unvarify_term: non-Var", [t])

fun decode_line sym_tab (Definition (name, phi1, phi2)) ctxt =
    let
      val thy = Proof_Context.theory_of ctxt
      val t1 = prop_from_atp ctxt true sym_tab phi1
      val vars = snd (strip_comb t1)
      val frees = map unvarify_term vars
      val unvarify_args = subst_atomic (vars ~~ frees)
      val t2 = prop_from_atp ctxt true sym_tab phi2
      val (t1, t2) =
        HOLogic.eq_const HOLogic.typeT $ t1 $ t2
        |> unvarify_args |> uncombine_term thy |> infer_formula_types ctxt
        |> HOLogic.dest_eq
    in
      (Definition (name, t1, t2),
       fold Variable.declare_term (maps Misc_Legacy.term_frees [t1, t2]) ctxt)
    end
  | decode_line sym_tab (Inference (name, u, rule, deps)) ctxt =
    let val t = u |> uncombined_etc_prop_from_atp ctxt true sym_tab in
      (Inference (name, t, rule, deps),
       fold Variable.declare_term (Misc_Legacy.term_frees t) ctxt)
    end
fun decode_lines ctxt sym_tab lines =
  fst (fold_map (decode_line sym_tab) lines ctxt)

fun is_same_inference _ (Definition _) = false
  | is_same_inference t (Inference (_, t', _, _)) = t aconv t'

(* No "real" literals means only type information (tfree_tcs, clsrel, or
   clsarity). *)
val is_only_type_information = curry (op aconv) HOLogic.true_const

fun replace_one_dependency (old, new) dep =
  if is_same_atp_step dep old then new else [dep]
fun replace_dependencies_in_line _ (line as Definition _) = line
  | replace_dependencies_in_line p (Inference (name, t, rule, deps)) =
    Inference (name, t, rule,
               fold (union (op =) o replace_one_dependency p) deps [])

(* Discard facts; consolidate adjacent lines that prove the same formula, since
   they differ only in type information.*)
fun add_line _ (line as Definition _) lines = line :: lines
  | add_line fact_names (Inference (name as (_, ss), t, rule, [])) lines =
    (* No dependencies: fact, conjecture, or (for Vampire) internal facts or
       definitions. *)
    if is_fact fact_names ss then
      (* Facts are not proof lines. *)
      if is_only_type_information t then
        map (replace_dependencies_in_line (name, [])) lines
      (* Is there a repetition? If so, replace later line by earlier one. *)
      else case take_prefix (not o is_same_inference t) lines of
        (_, []) => lines (* no repetition of proof line *)
      | (pre, Inference (name', _, _, _) :: post) =>
        pre @ map (replace_dependencies_in_line (name', [name])) post
      | _ => raise Fail "unexpected inference"
    else if is_conjecture ss then
      Inference (name, s_not t, rule, []) :: lines
    else
      map (replace_dependencies_in_line (name, [])) lines
  | add_line _ (Inference (name, t, rule, deps)) lines =
    (* Type information will be deleted later; skip repetition test. *)
    if is_only_type_information t then
      Inference (name, t, rule, deps) :: lines
    (* Is there a repetition? If so, replace later line by earlier one. *)
    else case take_prefix (not o is_same_inference t) lines of
      (* FIXME: Doesn't this code risk conflating proofs involving different
         types? *)
       (_, []) => Inference (name, t, rule, deps) :: lines
     | (pre, Inference (name', t', rule, _) :: post) =>
       Inference (name, t', rule, deps) ::
       pre @ map (replace_dependencies_in_line (name', [name])) post
     | _ => raise Fail "unexpected inference"

(* Recursively delete empty lines (type information) from the proof. *)
fun add_nontrivial_line (line as Inference (name, t, _, [])) lines =
    if is_only_type_information t then delete_dependency name lines
    else line :: lines
  | add_nontrivial_line line lines = line :: lines
and delete_dependency name lines =
  fold_rev add_nontrivial_line
           (map (replace_dependencies_in_line (name, [])) lines) []

(* ATPs sometimes reuse free variable names in the strangest ways. Removing
   offending lines often does the trick. *)
fun is_bad_free frees (Free x) = not (member (op =) frees x)
  | is_bad_free _ _ = false

fun add_desired_line _ _ _ (line as Definition (name, _, _)) (j, lines) =
    (j, line :: map (replace_dependencies_in_line (name, [])) lines)
  | add_desired_line isar_shrink_factor fact_names frees
                     (Inference (name as (_, ss), t, rule, deps)) (j, lines) =
    (j + 1,
     if is_fact fact_names ss orelse
        is_conjecture ss orelse
        (* the last line must be kept *)
        j = 0 orelse
        (not (is_only_type_information t) andalso
         null (Term.add_tvars t []) andalso
         not (exists_subterm (is_bad_free frees) t) andalso
         length deps >= 2 andalso j mod isar_shrink_factor = 0 andalso
         (* kill next to last line, which usually results in a trivial step *)
         j <> 1) then
       Inference (name, t, rule, deps) :: lines  (* keep line *)
     else
       map (replace_dependencies_in_line (name, deps)) lines)  (* drop line *)

(** Isar proof construction and manipulation **)

fun merge_fact_sets (ls1, ss1) (ls2, ss2) =
  (union (op =) ls1 ls2, union (op =) ss1 ss2)

type label = string * int
type facts = label list * string list

datatype isar_qualifier = Show | Then | Moreover | Ultimately

datatype isar_step =
  Fix of (string * typ) list |
  Let of term * term |
  Assume of label * term |
  Have of isar_qualifier list * label * term * byline
and byline =
  ByMetis of facts |
  CaseSplit of isar_step list list * facts

fun smart_case_split [] facts = ByMetis facts
  | smart_case_split proofs facts = CaseSplit (proofs, facts)

fun add_fact_from_dependency fact_names (name as (_, ss)) =
  if is_fact fact_names ss then
    apsnd (union (op =) (map fst (resolve_fact fact_names ss)))
  else
    apfst (insert (op =) (raw_label_for_name name))

fun step_for_line _ _ (Definition (_, t1, t2)) = Let (t1, t2)
  | step_for_line _ _ (Inference (name, t, _, [])) =
    Assume (raw_label_for_name name, t)
  | step_for_line fact_names j (Inference (name, t, _, deps)) =
    Have (if j = 1 then [Show] else [], raw_label_for_name name,
          fold_rev forall_of (map Var (Term.add_vars t [])) t,
          ByMetis (fold (add_fact_from_dependency fact_names) deps ([], [])))

fun repair_name "$true" = "c_True"
  | repair_name "$false" = "c_False"
  | repair_name "$$e" = tptp_equal (* seen in Vampire proofs *)
  | repair_name s =
    if is_tptp_equal s orelse
       (* seen in Vampire proofs *)
       (String.isPrefix "sQ" s andalso String.isSuffix "_eqProxy" s) then
      tptp_equal
    else
      s

fun isar_proof_from_atp_proof pool ctxt isar_shrink_factor fact_names sym_tab
                              params frees atp_proof =
  let
    val lines =
      atp_proof
      |> clean_up_atp_proof_dependencies
      |> nasty_atp_proof pool
      |> map_term_names_in_atp_proof repair_name
      |> decode_lines ctxt sym_tab
      |> rpair [] |-> fold_rev (add_line fact_names)
      |> rpair [] |-> fold_rev add_nontrivial_line
      |> rpair (0, [])
      |-> fold_rev (add_desired_line isar_shrink_factor fact_names frees)
      |> snd
  in
    (if null params then [] else [Fix params]) @
    map2 (step_for_line fact_names) (length lines downto 1) lines
  end

(* When redirecting proofs, we keep information about the labels seen so far in
   the "backpatches" data structure. The first component indicates which facts
   should be associated with forthcoming proof steps. The second component is a
   pair ("assum_ls", "drop_ls"), where "assum_ls" are the labels that should
   become assumptions and "drop_ls" are the labels that should be dropped in a
   case split. *)
type backpatches = (label * facts) list * (label list * label list)

fun used_labels_of_step (Have (_, _, _, by)) =
    (case by of
       ByMetis (ls, _) => ls
     | CaseSplit (proofs, (ls, _)) =>
       fold (union (op =) o used_labels_of) proofs ls)
  | used_labels_of_step _ = []
and used_labels_of proof = fold (union (op =) o used_labels_of_step) proof []

fun new_labels_of_step (Fix _) = []
  | new_labels_of_step (Let _) = []
  | new_labels_of_step (Assume (l, _)) = [l]
  | new_labels_of_step (Have (_, l, _, _)) = [l]
val new_labels_of = maps new_labels_of_step

val join_proofs =
  let
    fun aux _ [] = NONE
      | aux proof_tail (proofs as (proof1 :: _)) =
        if exists null proofs then
          NONE
        else if forall (curry (op =) (hd proof1) o hd) (tl proofs) then
          aux (hd proof1 :: proof_tail) (map tl proofs)
        else case hd proof1 of
          Have ([], l, t, _) => (* FIXME: should we really ignore the "by"? *)
          if forall (fn Have ([], l', t', _) :: _ => (l, t) = (l', t')
                      | _ => false) (tl proofs) andalso
             not (exists (member (op =) (maps new_labels_of proofs))
                         (used_labels_of proof_tail)) then
            SOME (l, t, map rev proofs, proof_tail)
          else
            NONE
        | _ => NONE
  in aux [] o map rev end

fun case_split_qualifiers proofs =
  case length proofs of
    0 => []
  | 1 => [Then]
  | _ => [Ultimately]

fun redirect_proof hyp_ts concl_t proof =
  let
    (* The first pass outputs those steps that are independent of the negated
       conjecture. The second pass flips the proof by contradiction to obtain a
       direct proof, introducing case splits when an inference depends on
       several facts that depend on the negated conjecture. *)
     val concl_l = (conjecture_prefix, length hyp_ts)
     fun first_pass ([], contra) = ([], contra)
       | first_pass ((step as Fix _) :: proof, contra) =
         first_pass (proof, contra) |>> cons step
       | first_pass ((step as Let _) :: proof, contra) =
         first_pass (proof, contra) |>> cons step
       | first_pass ((step as Assume (l as (_, j), _)) :: proof, contra) =
         if l = concl_l then first_pass (proof, contra ||> cons step)
         else first_pass (proof, contra) |>> cons (Assume (l, nth hyp_ts j))
       | first_pass (Have (qs, l, t, ByMetis (ls, ss)) :: proof, contra) =
         let val step = Have (qs, l, t, ByMetis (ls, ss)) in
           if exists (member (op =) (fst contra)) ls then
             first_pass (proof, contra |>> cons l ||> cons step)
           else
             first_pass (proof, contra) |>> cons step
         end
       | first_pass _ = raise Fail "malformed proof"
    val (proof_top, (contra_ls, contra_proof)) =
      first_pass (proof, ([concl_l], []))
    val backpatch_label = the_default ([], []) oo AList.lookup (op =) o fst
    fun backpatch_labels patches ls =
      fold merge_fact_sets (map (backpatch_label patches) ls) ([], [])
    fun second_pass end_qs ([], assums, patches) =
        ([Have (end_qs, no_label, concl_t,
                ByMetis (backpatch_labels patches (map snd assums)))], patches)
      | second_pass end_qs (Assume (l, t) :: proof, assums, patches) =
        second_pass end_qs (proof, (t, l) :: assums, patches)
      | second_pass end_qs (Have (qs, l, t, ByMetis (ls, ss)) :: proof, assums,
                            patches) =
        (if member (op =) (snd (snd patches)) l andalso
            not (member (op =) (fst (snd patches)) l) andalso
            not (AList.defined (op =) (fst patches) l) then
           second_pass end_qs (proof, assums, patches ||> apsnd (append ls))
         else case List.partition (member (op =) contra_ls) ls of
           ([contra_l], co_ls) =>
           if member (op =) qs Show then
             second_pass end_qs (proof, assums,
                                 patches |>> cons (contra_l, (co_ls, ss)))
           else
             second_pass end_qs
                         (proof, assums,
                          patches |>> cons (contra_l, (l :: co_ls, ss)))
             |>> cons (if member (op =) (fst (snd patches)) l then
                         Assume (l, s_not t)
                       else
                         Have (qs, l, s_not t,
                               ByMetis (backpatch_label patches l)))
         | (contra_ls as _ :: _, co_ls) =>
           let
             val proofs =
               map_filter
                   (fn l =>
                       if l = concl_l then
                         NONE
                       else
                         let
                           val drop_ls = filter (curry (op <>) l) contra_ls
                         in
                           second_pass []
                               (proof, assums,
                                patches ||> apfst (insert (op =) l)
                                        ||> apsnd (union (op =) drop_ls))
                           |> fst |> SOME
                         end) contra_ls
             val (assumes, facts) =
               if member (op =) (fst (snd patches)) l then
                 ([Assume (l, s_not t)], (l :: co_ls, ss))
               else
                 ([], (co_ls, ss))
           in
             (case join_proofs proofs of
                SOME (l, t, proofs, proof_tail) =>
                Have (case_split_qualifiers proofs @
                      (if null proof_tail then end_qs else []), l, t,
                      smart_case_split proofs facts) :: proof_tail
              | NONE =>
                [Have (case_split_qualifiers proofs @ end_qs, no_label,
                       concl_t, smart_case_split proofs facts)],
              patches)
             |>> append assumes
           end
         | _ => raise Fail "malformed proof")
       | second_pass _ _ = raise Fail "malformed proof"
    val proof_bottom =
      second_pass [Show] (contra_proof, [], ([], ([], []))) |> fst
  in proof_top @ proof_bottom end

(* FIXME: Still needed? Probably not. *)
val kill_duplicate_assumptions_in_proof =
  let
    fun relabel_facts subst =
      apfst (map (fn l => AList.lookup (op =) subst l |> the_default l))
    fun do_step (step as Assume (l, t)) (proof, subst, assums) =
        (case AList.lookup (op aconv) assums t of
           SOME l' => (proof, (l, l') :: subst, assums)
         | NONE => (step :: proof, subst, (t, l) :: assums))
      | do_step (Have (qs, l, t, by)) (proof, subst, assums) =
        (Have (qs, l, t,
               case by of
                 ByMetis facts => ByMetis (relabel_facts subst facts)
               | CaseSplit (proofs, facts) =>
                 CaseSplit (map do_proof proofs, relabel_facts subst facts)) ::
         proof, subst, assums)
      | do_step step (proof, subst, assums) = (step :: proof, subst, assums)
    and do_proof proof = fold do_step proof ([], [], []) |> #1 |> rev
  in do_proof end

val then_chain_proof =
  let
    fun aux _ [] = []
      | aux _ ((step as Assume (l, _)) :: proof) = step :: aux l proof
      | aux l' (Have (qs, l, t, by) :: proof) =
        (case by of
           ByMetis (ls, ss) =>
           Have (if member (op =) ls l' then
                   (Then :: qs, l, t,
                    ByMetis (filter_out (curry (op =) l') ls, ss))
                 else
                   (qs, l, t, ByMetis (ls, ss)))
         | CaseSplit (proofs, facts) =>
           Have (qs, l, t, CaseSplit (map (aux no_label) proofs, facts))) ::
        aux l proof
      | aux _ (step :: proof) = step :: aux no_label proof
  in aux no_label end

fun kill_useless_labels_in_proof proof =
  let
    val used_ls = used_labels_of proof
    fun do_label l = if member (op =) used_ls l then l else no_label
    fun do_step (Assume (l, t)) = Assume (do_label l, t)
      | do_step (Have (qs, l, t, by)) =
        Have (qs, do_label l, t,
              case by of
                CaseSplit (proofs, facts) =>
                CaseSplit (map (map do_step) proofs, facts)
              | _ => by)
      | do_step step = step
  in map do_step proof end

fun prefix_for_depth n = replicate_string (n + 1)

val relabel_proof =
  let
    fun aux _ _ _ [] = []
      | aux subst depth (next_assum, next_fact) (Assume (l, t) :: proof) =
        if l = no_label then
          Assume (l, t) :: aux subst depth (next_assum, next_fact) proof
        else
          let val l' = (prefix_for_depth depth assum_prefix, next_assum) in
            Assume (l', t) ::
            aux ((l, l') :: subst) depth (next_assum + 1, next_fact) proof
          end
      | aux subst depth (next_assum, next_fact) (Have (qs, l, t, by) :: proof) =
        let
          val (l', subst, next_fact) =
            if l = no_label then
              (l, subst, next_fact)
            else
              let
                val l' = (prefix_for_depth depth have_prefix, next_fact)
              in (l', (l, l') :: subst, next_fact + 1) end
          val relabel_facts =
            apfst (maps (the_list o AList.lookup (op =) subst))
          val by =
            case by of
              ByMetis facts => ByMetis (relabel_facts facts)
            | CaseSplit (proofs, facts) =>
              CaseSplit (map (aux subst (depth + 1) (1, 1)) proofs,
                         relabel_facts facts)
        in
          Have (qs, l', t, by) ::
          aux subst depth (next_assum, next_fact) proof
        end
      | aux subst depth nextp (step :: proof) =
        step :: aux subst depth nextp proof
  in aux [] 0 (1, 1) end

fun string_for_proof ctxt0 type_enc lam_trans i n =
  let
    val ctxt =
      ctxt0 |> Config.put show_free_types false
            |> Config.put show_types true
            |> Config.put show_sorts true
    fun fix_print_mode f x =
      Print_Mode.setmp (filter (curry (op =) Symbol.xsymbolsN)
                               (print_mode_value ())) f x
    fun do_indent ind = replicate_string (ind * indent_size) " "
    fun do_free (s, T) =
      maybe_quote s ^ " :: " ^
      maybe_quote (fix_print_mode (Syntax.string_of_typ ctxt) T)
    fun do_label l = if l = no_label then "" else string_for_label l ^ ": "
    fun do_have qs =
      (if member (op =) qs Moreover then "moreover " else "") ^
      (if member (op =) qs Ultimately then "ultimately " else "") ^
      (if member (op =) qs Then then
         if member (op =) qs Show then "thus" else "hence"
       else
         if member (op =) qs Show then "show" else "have")
    val do_term = maybe_quote o fix_print_mode (Syntax.string_of_term ctxt)
    val reconstr = Metis (type_enc, lam_trans)
    fun do_facts (ls, ss) =
      reconstructor_command reconstr 1 1
          (ls |> sort_distinct (prod_ord string_ord int_ord),
           ss |> sort_distinct string_ord)
    and do_step ind (Fix xs) =
        do_indent ind ^ "fix " ^ space_implode " and " (map do_free xs) ^ "\n"
      | do_step ind (Let (t1, t2)) =
        do_indent ind ^ "let " ^ do_term t1 ^ " = " ^ do_term t2 ^ "\n"
      | do_step ind (Assume (l, t)) =
        do_indent ind ^ "assume " ^ do_label l ^ do_term t ^ "\n"
      | do_step ind (Have (qs, l, t, ByMetis facts)) =
        do_indent ind ^ do_have qs ^ " " ^
        do_label l ^ do_term t ^ " " ^ do_facts facts ^ "\n"
      | do_step ind (Have (qs, l, t, CaseSplit (proofs, facts))) =
        space_implode (do_indent ind ^ "moreover\n")
                      (map (do_block ind) proofs) ^
        do_indent ind ^ do_have qs ^ " " ^ do_label l ^ do_term t ^ " " ^
        do_facts facts ^ "\n"
    and do_steps prefix suffix ind steps =
      let val s = implode (map (do_step ind) steps) in
        replicate_string (ind * indent_size - size prefix) " " ^ prefix ^
        String.extract (s, ind * indent_size,
                        SOME (size s - ind * indent_size - 1)) ^
        suffix ^ "\n"
      end
    and do_block ind proof = do_steps "{ " " }" (ind + 1) proof
    (* One-step proofs are pointless; better use the Metis one-liner
       directly. *)
    and do_proof [Have (_, _, _, ByMetis _)] = ""
      | do_proof proof =
        (if i <> 1 then "prefer " ^ string_of_int i ^ "\n" else "") ^
        do_indent 0 ^ "proof -\n" ^ do_steps "" "" 1 proof ^ do_indent 0 ^
        (if n <> 1 then "next" else "qed")
  in do_proof end

fun isar_proof_text ctxt isar_proof_requested
        (debug, isar_shrink_factor, pool, fact_names, sym_tab, atp_proof, goal)
        (one_line_params as (_, _, _, _, subgoal, subgoal_count)) =
  let
    val isar_shrink_factor =
      (if isar_proof_requested then 1 else 2) * isar_shrink_factor
    val (params, hyp_ts, concl_t) = strip_subgoal ctxt goal subgoal
    val frees = fold Term.add_frees (concl_t :: hyp_ts) []
    val one_line_proof = one_line_proof_text one_line_params
    val type_enc =
      if is_typed_helper_used_in_atp_proof atp_proof then full_typesN
      else partial_typesN
    val lam_trans = lam_trans_from_atp_proof atp_proof metis_default_lam_trans
    fun isar_proof_for () =
      case atp_proof
           |> isar_proof_from_atp_proof pool ctxt isar_shrink_factor fact_names
                                        sym_tab params frees
           |> redirect_proof hyp_ts concl_t
           |> kill_duplicate_assumptions_in_proof
           |> then_chain_proof
           |> kill_useless_labels_in_proof
           |> relabel_proof
           |> string_for_proof ctxt type_enc lam_trans subgoal subgoal_count of
        "" =>
        if isar_proof_requested then
          "\nNo structured proof available (proof too short)."
        else
          ""
      | proof =>
        "\n\n" ^ (if isar_proof_requested then "Structured proof"
                  else "Perhaps this will work") ^
        ":\n" ^ Markup.markup Markup.sendback proof
    val isar_proof =
      if debug then
        isar_proof_for ()
      else
        case try isar_proof_for () of
          SOME s => s
        | NONE => if isar_proof_requested then
                    "\nWarning: The Isar proof construction failed."
                  else
                    ""
  in one_line_proof ^ isar_proof end

fun proof_text ctxt isar_proof isar_params
               (one_line_params as (preplay, _, _, _, _, _)) =
  (if case preplay of Failed_to_Play _ => true | _ => isar_proof then
     isar_proof_text ctxt isar_proof isar_params
   else
     one_line_proof_text) one_line_params

end;