src/HOL/Tools/Sledgehammer/sledgehammer_filter.ML
author blanchet
Wed, 21 Sep 2011 15:55:15 +0200
changeset 45034 b0f61dec677a
parent 44934 2302faa4ae0e
child 45301 866b075aa99b
permissions -rw-r--r--
tuned comment

(*  Title:      HOL/Tools/Sledgehammer/sledgehammer_filter.ML
    Author:     Jia Meng, Cambridge University Computer Laboratory and NICTA
    Author:     Jasmin Blanchette, TU Muenchen

Sledgehammer's relevance filter.
*)

signature SLEDGEHAMMER_FILTER =
sig
  type locality = ATP_Translate.locality

  type relevance_fudge =
    {local_const_multiplier : real,
     worse_irrel_freq : real,
     higher_order_irrel_weight : real,
     abs_rel_weight : real,
     abs_irrel_weight : real,
     skolem_irrel_weight : real,
     theory_const_rel_weight : real,
     theory_const_irrel_weight : real,
     chained_const_irrel_weight : real,
     intro_bonus : real,
     elim_bonus : real,
     simp_bonus : real,
     local_bonus : real,
     assum_bonus : real,
     chained_bonus : real,
     max_imperfect : real,
     max_imperfect_exp : real,
     threshold_divisor : real,
     ridiculous_threshold : real}

  type relevance_override =
    {add : (Facts.ref * Attrib.src list) list,
     del : (Facts.ref * Attrib.src list) list,
     only : bool}

  val trace : bool Config.T
  val ignore_no_atp : bool Config.T
  val instantiate_inducts : bool Config.T
  val no_relevance_override : relevance_override
  val const_names_in_fact :
    theory -> (string * typ -> term list -> bool * term list) -> term
    -> string list
  val fact_from_ref :
    Proof.context -> unit Symtab.table -> thm list
    -> Facts.ref * Attrib.src list -> ((string * locality) * thm) list
  val all_facts :
    Proof.context -> bool -> 'a Symtab.table -> bool -> thm list -> thm list
    -> (((unit -> string) * locality) * thm) list
  val nearly_all_facts :
    Proof.context -> bool -> relevance_override -> thm list -> term list -> term
    -> (((unit -> string) * locality) * thm) list
  val relevant_facts :
    Proof.context -> real * real -> int
    -> (string * typ -> term list -> bool * term list) -> relevance_fudge
    -> relevance_override -> thm list -> term list -> term
    -> (((unit -> string) * locality) * thm) list
    -> ((string * locality) * thm) list
end;

structure Sledgehammer_Filter : SLEDGEHAMMER_FILTER =
struct

open ATP_Translate
open Metis_Tactic
open Sledgehammer_Util

val trace =
  Attrib.setup_config_bool @{binding sledgehammer_filter_trace} (K false)
fun trace_msg ctxt msg = if Config.get ctxt trace then tracing (msg ()) else ()

(* experimental features *)
val ignore_no_atp =
  Attrib.setup_config_bool @{binding sledgehammer_ignore_no_atp} (K false)
val instantiate_inducts =
  Attrib.setup_config_bool @{binding sledgehammer_instantiate_inducts} (K false)

type relevance_fudge =
  {local_const_multiplier : real,
   worse_irrel_freq : real,
   higher_order_irrel_weight : real,
   abs_rel_weight : real,
   abs_irrel_weight : real,
   skolem_irrel_weight : real,
   theory_const_rel_weight : real,
   theory_const_irrel_weight : real,
   chained_const_irrel_weight : real,
   intro_bonus : real,
   elim_bonus : real,
   simp_bonus : real,
   local_bonus : real,
   assum_bonus : real,
   chained_bonus : real,
   max_imperfect : real,
   max_imperfect_exp : real,
   threshold_divisor : real,
   ridiculous_threshold : real}

type relevance_override =
  {add : (Facts.ref * Attrib.src list) list,
   del : (Facts.ref * Attrib.src list) list,
   only : bool}

val no_relevance_override = {add = [], del = [], only = false}

val sledgehammer_prefix = "Sledgehammer" ^ Long_Name.separator
val abs_name = sledgehammer_prefix ^ "abs"
val skolem_prefix = sledgehammer_prefix ^ "sko"
val theory_const_suffix = Long_Name.separator ^ " 1"

fun needs_quoting reserved s =
  Symtab.defined reserved s orelse
  exists (not o Lexicon.is_identifier) (Long_Name.explode s)

fun make_name reserved multi j name =
  (name |> needs_quoting reserved name ? quote) ^
  (if multi then "(" ^ string_of_int j ^ ")" else "")

fun explode_interval _ (Facts.FromTo (i, j)) = i upto j
  | explode_interval max (Facts.From i) = i upto i + max - 1
  | explode_interval _ (Facts.Single i) = [i]

val backquote =
  raw_explode #> map (fn "`" => "\\`" | s => s) #> implode #> enclose "`" "`"
fun fact_from_ref ctxt reserved chained_ths (xthm as (xref, args)) =
  let
    val ths = Attrib.eval_thms ctxt [xthm]
    val bracket =
      map (enclose "[" "]" o Pretty.str_of o Args.pretty_src ctxt) args
      |> implode
    fun nth_name j =
      case xref of
        Facts.Fact s => backquote s ^ bracket
      | Facts.Named (("", _), _) => "[" ^ bracket ^ "]"
      | Facts.Named ((name, _), NONE) =>
        make_name reserved (length ths > 1) (j + 1) name ^ bracket
      | Facts.Named ((name, _), SOME intervals) =>
        make_name reserved true
                 (nth (maps (explode_interval (length ths)) intervals) j) name ^
        bracket
  in
    (ths, (0, []))
    |-> fold (fn th => fn (j, rest) =>
                 (j + 1,
                  ((nth_name j,
                    if member Thm.eq_thm_prop chained_ths th then Chained
                    else General), th) :: rest))
    |> snd
  end

(* This is a terrible hack. Free variables are sometimes coded as "M__" when
   they are displayed as "M" and we want to avoid clashes with these. But
   sometimes it's even worse: "Ma__" encodes "M". So we simply reserve all
   prefixes of all free variables. In the worse case scenario, where the fact
   won't be resolved correctly, the user can fix it manually, e.g., by naming
   the fact in question. Ideally we would need nothing of it, but backticks
   simply don't work with schematic variables. *)
fun all_prefixes_of s =
  map (fn i => String.extract (s, 0, SOME i)) (1 upto size s - 1)
fun close_form t =
  (t, [] |> Term.add_free_names t |> maps all_prefixes_of)
  |> fold (fn ((s, i), T) => fn (t', taken) =>
              let val s' = singleton (Name.variant_list taken) s in
                ((if fastype_of t' = HOLogic.boolT then HOLogic.all_const
                  else Term.all) T
                 $ Abs (s', T, abstract_over (Var ((s, i), T), t')),
                 s' :: taken)
              end)
          (Term.add_vars t [] |> sort_wrt (fst o fst))
  |> fst

fun string_for_term ctxt t =
  Print_Mode.setmp (filter (curry (op =) Symbol.xsymbolsN)
                   (print_mode_value ())) (Syntax.string_of_term ctxt) t
  |> String.translate (fn c => if Char.isPrint c then str c else "")
  |> simplify_spaces

(** Structural induction rules **)

fun struct_induct_rule_on th =
  case Logic.strip_horn (prop_of th) of
    (prems, @{const Trueprop}
            $ ((p as Var ((p_name, 0), _)) $ (a as Var (_, ind_T)))) =>
    if not (is_TVar ind_T) andalso length prems > 1 andalso
       exists (exists_subterm (curry (op aconv) p)) prems andalso
       not (exists (exists_subterm (curry (op aconv) a)) prems) then
      SOME (p_name, ind_T)
    else
      NONE
  | _ => NONE

fun instantiate_induct_rule ctxt concl_prop p_name ((name, loc), th) ind_x =
  let
    fun varify_noninducts (t as Free (s, T)) =
        if (s, T) = ind_x orelse can dest_funT T then t else Var ((s, 0), T)
      | varify_noninducts t = t
    val p_inst =
      concl_prop |> map_aterms varify_noninducts |> close_form
                 |> lambda (Free ind_x)
                 |> string_for_term ctxt
  in
    ((fn () => name () ^ "[where " ^ p_name ^ " = " ^ quote p_inst ^ "]", loc),
     th |> read_instantiate ctxt [((p_name, 0), p_inst)])
  end

fun type_match thy (T1, T2) =
  (Sign.typ_match thy (T2, T1) Vartab.empty; true)
  handle Type.TYPE_MATCH => false

fun instantiate_if_induct_rule ctxt stmt stmt_xs (ax as (_, th)) =
  case struct_induct_rule_on th of
    SOME (p_name, ind_T) =>
    let val thy = Proof_Context.theory_of ctxt in
      stmt_xs |> filter (fn (_, T) => type_match thy (T, ind_T))
              |> map_filter (try (instantiate_induct_rule ctxt stmt p_name ax))
    end
  | NONE => [ax]

(***************************************************************)
(* Relevance Filtering                                         *)
(***************************************************************)

(*** constants with types ***)

fun order_of_type (Type (@{type_name fun}, [T1, @{typ bool}])) =
    order_of_type T1 (* cheat: pretend sets are first-order *)
  | order_of_type (Type (@{type_name fun}, [T1, T2])) =
    Int.max (order_of_type T1 + 1, order_of_type T2)
  | order_of_type (Type (_, Ts)) = fold (Integer.max o order_of_type) Ts 0
  | order_of_type _ = 0

(* An abstraction of Isabelle types and first-order terms *)
datatype pattern = PVar | PApp of string * pattern list
datatype ptype = PType of int * pattern list

fun string_for_pattern PVar = "_"
  | string_for_pattern (PApp (s, ps)) =
    if null ps then s else s ^ string_for_patterns ps
and string_for_patterns ps = "(" ^ commas (map string_for_pattern ps) ^ ")"
fun string_for_ptype (PType (_, ps)) = string_for_patterns ps

(*Is the second type an instance of the first one?*)
fun match_pattern (PVar, _) = true
  | match_pattern (PApp _, PVar) = false
  | match_pattern (PApp (s, ps), PApp (t, qs)) =
    s = t andalso match_patterns (ps, qs)
and match_patterns (_, []) = true
  | match_patterns ([], _) = false
  | match_patterns (p :: ps, q :: qs) =
    match_pattern (p, q) andalso match_patterns (ps, qs)
fun match_ptype (PType (_, ps), PType (_, qs)) = match_patterns (ps, qs)

(* Is there a unifiable constant? *)
fun pconst_mem f consts (s, ps) =
  exists (curry (match_ptype o f) ps)
         (map snd (filter (curry (op =) s o fst) consts))
fun pconst_hyper_mem f const_tab (s, ps) =
  exists (curry (match_ptype o f) ps) (these (Symtab.lookup const_tab s))

fun pattern_for_type (Type (s, Ts)) = PApp (s, map pattern_for_type Ts)
  | pattern_for_type (TFree (s, _)) = PApp (s, [])
  | pattern_for_type (TVar _) = PVar

(* Pairs a constant with the list of its type instantiations. *)
fun ptype thy const x =
  (if const then map pattern_for_type (these (try (Sign.const_typargs thy) x))
   else [])
fun rich_ptype thy const (s, T) =
  PType (order_of_type T, ptype thy const (s, T))
fun rich_pconst thy const (s, T) = (s, rich_ptype thy const (s, T))

fun string_for_hyper_pconst (s, ps) =
  s ^ "{" ^ commas (map string_for_ptype ps) ^ "}"

(* Add a pconstant to the table, but a [] entry means a standard
   connective, which we ignore.*)
fun add_pconst_to_table also_skolem (s, p) =
  if (not also_skolem andalso String.isPrefix skolem_prefix s) then I
  else Symtab.map_default (s, [p]) (insert (op =) p)

(* Set constants tend to pull in too many irrelevant facts. We limit the damage
   by treating them more or less as if they were built-in but add their
   definition at the end. *)
val set_consts =
  [(@{const_name Collect}, @{thms Collect_def}),
   (@{const_name Set.member}, @{thms mem_def})]

val is_set_const = AList.defined (op =) set_consts

fun add_pconsts_in_term thy is_built_in_const also_skolems pos =
  let
    val flip = Option.map not
    (* We include free variables, as well as constants, to handle locales. For
       each quantifiers that must necessarily be skolemized by the automatic
       prover, we introduce a fresh constant to simulate the effect of
       Skolemization. *)
    fun do_const const ext_arg (x as (s, _)) ts =
      let val (built_in, ts) = is_built_in_const x ts in
        if is_set_const s then
          fold (do_term ext_arg) ts
        else
          (not built_in
           ? add_pconst_to_table also_skolems (rich_pconst thy const x))
          #> fold (do_term false) ts
      end
    and do_term ext_arg t =
      case strip_comb t of
        (Const x, ts) => do_const true ext_arg x ts
      | (Free x, ts) => do_const false ext_arg x ts
      | (Abs (_, T, t'), ts) =>
        ((null ts andalso not ext_arg)
         (* Since lambdas on the right-hand side of equalities are usually
            extensionalized later by "extensionalize_term", we don't penalize
            them here. *)
         ? add_pconst_to_table true (abs_name, PType (order_of_type T + 1, [])))
        #> fold (do_term false) (t' :: ts)
      | (_, ts) => fold (do_term false) ts
    fun do_quantifier will_surely_be_skolemized abs_T body_t =
      do_formula pos body_t
      #> (if also_skolems andalso will_surely_be_skolemized then
            add_pconst_to_table true
                (legacy_gensym skolem_prefix, PType (order_of_type abs_T, []))
          else
            I)
    and do_term_or_formula ext_arg T =
      if T = HOLogic.boolT then do_formula NONE else do_term ext_arg
    and do_formula pos t =
      case t of
        Const (@{const_name all}, _) $ Abs (_, T, t') =>
        do_quantifier (pos = SOME false) T t'
      | @{const "==>"} $ t1 $ t2 =>
        do_formula (flip pos) t1 #> do_formula pos t2
      | Const (@{const_name "=="}, Type (_, [T, _])) $ t1 $ t2 =>
        do_term_or_formula false T t1 #> do_term_or_formula true T t2
      | @{const Trueprop} $ t1 => do_formula pos t1
      | @{const False} => I
      | @{const True} => I
      | @{const Not} $ t1 => do_formula (flip pos) t1
      | Const (@{const_name All}, _) $ Abs (_, T, t') =>
        do_quantifier (pos = SOME false) T t'
      | Const (@{const_name Ex}, _) $ Abs (_, T, t') =>
        do_quantifier (pos = SOME true) T t'
      | @{const HOL.conj} $ t1 $ t2 => fold (do_formula pos) [t1, t2]
      | @{const HOL.disj} $ t1 $ t2 => fold (do_formula pos) [t1, t2]
      | @{const HOL.implies} $ t1 $ t2 =>
        do_formula (flip pos) t1 #> do_formula pos t2
      | Const (@{const_name HOL.eq}, Type (_, [T, _])) $ t1 $ t2 =>
        do_term_or_formula false T t1 #> do_term_or_formula true T t2
      | Const (@{const_name If}, Type (_, [_, Type (_, [T, _])]))
        $ t1 $ t2 $ t3 =>
        do_formula NONE t1 #> fold (do_term_or_formula false T) [t2, t3]
      | Const (@{const_name Ex1}, _) $ Abs (_, T, t') =>
        do_quantifier (is_some pos) T t'
      | Const (@{const_name Ball}, _) $ t1 $ Abs (_, T, t') =>
        do_quantifier (pos = SOME false) T
                      (HOLogic.mk_imp (incr_boundvars 1 t1 $ Bound 0, t'))
      | Const (@{const_name Bex}, _) $ t1 $ Abs (_, T, t') =>
        do_quantifier (pos = SOME true) T
                      (HOLogic.mk_conj (incr_boundvars 1 t1 $ Bound 0, t'))
      | (t0 as Const (_, @{typ bool})) $ t1 =>
        do_term false t0 #> do_formula pos t1  (* theory constant *)
      | _ => do_term false t
  in do_formula pos end

(*Inserts a dummy "constant" referring to the theory name, so that relevance
  takes the given theory into account.*)
fun theory_constify ({theory_const_rel_weight, theory_const_irrel_weight, ...}
                     : relevance_fudge) thy_name t =
  if exists (curry (op <) 0.0) [theory_const_rel_weight,
                                theory_const_irrel_weight] then
    Const (thy_name ^ theory_const_suffix, @{typ bool}) $ t
  else
    t

fun theory_const_prop_of fudge th =
  theory_constify fudge (Context.theory_name (theory_of_thm th)) (prop_of th)

(**** Constant / Type Frequencies ****)

(* A two-dimensional symbol table counts frequencies of constants. It's keyed
   first by constant name and second by its list of type instantiations. For the
   latter, we need a linear ordering on "pattern list". *)

fun pattern_ord p =
  case p of
    (PVar, PVar) => EQUAL
  | (PVar, PApp _) => LESS
  | (PApp _, PVar) => GREATER
  | (PApp q1, PApp q2) =>
    prod_ord fast_string_ord (dict_ord pattern_ord) (q1, q2)
fun ptype_ord (PType p, PType q) =
  prod_ord (dict_ord pattern_ord) int_ord (swap p, swap q)

structure PType_Tab = Table(type key = ptype val ord = ptype_ord)

fun count_fact_consts thy fudge =
  let
    fun do_const const (s, T) ts =
      (* Two-dimensional table update. Constant maps to types maps to count. *)
      PType_Tab.map_default (rich_ptype thy const (s, T), 0) (Integer.add 1)
      |> Symtab.map_default (s, PType_Tab.empty)
      #> fold do_term ts
    and do_term t =
      case strip_comb t of
        (Const x, ts) => do_const true x ts
      | (Free x, ts) => do_const false x ts
      | (Abs (_, _, t'), ts) => fold do_term (t' :: ts)
      | (_, ts) => fold do_term ts
  in do_term o theory_const_prop_of fudge o snd end


(**** Actual Filtering Code ****)

fun pow_int _ 0 = 1.0
  | pow_int x 1 = x
  | pow_int x n = if n > 0 then x * pow_int x (n - 1) else pow_int x (n + 1) / x

(*The frequency of a constant is the sum of those of all instances of its type.*)
fun pconst_freq match const_tab (c, ps) =
  PType_Tab.fold (fn (qs, m) => match (ps, qs) ? Integer.add m)
                 (the (Symtab.lookup const_tab c)) 0


(* A surprising number of theorems contain only a few significant constants.
   These include all induction rules, and other general theorems. *)

(* "log" seems best in practice. A constant function of one ignores the constant
   frequencies. Rare constants give more points if they are relevant than less
   rare ones. *)
fun rel_weight_for _ freq = 1.0 + 2.0 / Math.ln (Real.fromInt freq + 1.0)

(* Irrelevant constants are treated differently. We associate lower penalties to
   very rare constants and very common ones -- the former because they can't
   lead to the inclusion of too many new facts, and the latter because they are
   so common as to be of little interest. *)
fun irrel_weight_for ({worse_irrel_freq, higher_order_irrel_weight, ...}
                      : relevance_fudge) order freq =
  let val (k, x) = worse_irrel_freq |> `Real.ceil in
    (if freq < k then Math.ln (Real.fromInt (freq + 1)) / Math.ln x
     else rel_weight_for order freq / rel_weight_for order k)
    * pow_int higher_order_irrel_weight (order - 1)
  end

fun multiplier_for_const_name local_const_multiplier s =
  if String.isSubstring "." s then 1.0 else local_const_multiplier

(* Computes a constant's weight, as determined by its frequency. *)
fun generic_pconst_weight local_const_multiplier abs_weight skolem_weight
                          theory_const_weight chained_const_weight weight_for f
                          const_tab chained_const_tab (c as (s, PType (m, _))) =
  if s = abs_name then
    abs_weight
  else if String.isPrefix skolem_prefix s then
    skolem_weight
  else if String.isSuffix theory_const_suffix s then
    theory_const_weight
  else
    multiplier_for_const_name local_const_multiplier s
    * weight_for m (pconst_freq (match_ptype o f) const_tab c)
    |> (if chained_const_weight < 1.0 andalso
           pconst_hyper_mem I chained_const_tab c then
          curry (op *) chained_const_weight
        else
          I)

fun rel_pconst_weight ({local_const_multiplier, abs_rel_weight,
                        theory_const_rel_weight, ...} : relevance_fudge)
                      const_tab =
  generic_pconst_weight local_const_multiplier abs_rel_weight 0.0
                        theory_const_rel_weight 0.0 rel_weight_for I const_tab
                        Symtab.empty

fun irrel_pconst_weight (fudge as {local_const_multiplier, abs_irrel_weight,
                                   skolem_irrel_weight,
                                   theory_const_irrel_weight,
                                   chained_const_irrel_weight, ...})
                        const_tab chained_const_tab =
  generic_pconst_weight local_const_multiplier abs_irrel_weight
                        skolem_irrel_weight theory_const_irrel_weight
                        chained_const_irrel_weight (irrel_weight_for fudge) swap
                        const_tab chained_const_tab

fun locality_bonus ({intro_bonus, ...} : relevance_fudge) Intro = intro_bonus
  | locality_bonus {elim_bonus, ...} Elim = elim_bonus
  | locality_bonus {simp_bonus, ...} Simp = simp_bonus
  | locality_bonus {local_bonus, ...} Local = local_bonus
  | locality_bonus {assum_bonus, ...} Assum = assum_bonus
  | locality_bonus {chained_bonus, ...} Chained = chained_bonus
  | locality_bonus _ _ = 0.0

fun is_odd_const_name s =
  s = abs_name orelse String.isPrefix skolem_prefix s orelse
  String.isSuffix theory_const_suffix s

fun fact_weight fudge loc const_tab relevant_consts chained_consts fact_consts =
  case fact_consts |> List.partition (pconst_hyper_mem I relevant_consts)
                   ||> filter_out (pconst_hyper_mem swap relevant_consts) of
    ([], _) => 0.0
  | (rel, irrel) =>
    if forall (forall (is_odd_const_name o fst)) [rel, irrel] then
      0.0
    else
      let
        val irrel = irrel |> filter_out (pconst_mem swap rel)
        val rel_weight =
          0.0 |> fold (curry (op +) o rel_pconst_weight fudge const_tab) rel
        val irrel_weight =
          ~ (locality_bonus fudge loc)
          |> fold (curry (op +)
                   o irrel_pconst_weight fudge const_tab chained_consts) irrel
        val res = rel_weight / (rel_weight + irrel_weight)
      in if Real.isFinite res then res else 0.0 end

fun pconsts_in_fact thy is_built_in_const t =
  Symtab.fold (fn (s, pss) => fold (cons o pair s) pss)
              (Symtab.empty |> add_pconsts_in_term thy is_built_in_const true
                                                   (SOME true) t) []

fun pair_consts_fact thy is_built_in_const fudge fact =
  case fact |> snd |> theory_const_prop_of fudge
            |> pconsts_in_fact thy is_built_in_const of
    [] => NONE
  | consts => SOME ((fact, consts), NONE)

val const_names_in_fact = map fst ooo pconsts_in_fact

type annotated_thm =
  (((unit -> string) * locality) * thm) * (string * ptype) list

fun take_most_relevant ctxt max_relevant remaining_max
        ({max_imperfect, max_imperfect_exp, ...} : relevance_fudge)
        (candidates : (annotated_thm * real) list) =
  let
    val max_imperfect =
      Real.ceil (Math.pow (max_imperfect,
                    Math.pow (Real.fromInt remaining_max
                              / Real.fromInt max_relevant, max_imperfect_exp)))
    val (perfect, imperfect) =
      candidates |> sort (Real.compare o swap o pairself snd)
                 |> take_prefix (fn (_, w) => w > 0.99999)
    val ((accepts, more_rejects), rejects) =
      chop max_imperfect imperfect |>> append perfect |>> chop remaining_max
  in
    trace_msg ctxt (fn () =>
        "Actually passed (" ^ string_of_int (length accepts) ^ " of " ^
        string_of_int (length candidates) ^ "): " ^
        (accepts |> map (fn ((((name, _), _), _), weight) =>
                            name () ^ " [" ^ Real.toString weight ^ "]")
                 |> commas));
    (accepts, more_rejects @ rejects)
  end

fun if_empty_replace_with_locality thy is_built_in_const facts loc tab =
  if Symtab.is_empty tab then
    Symtab.empty
    |> fold (add_pconsts_in_term thy is_built_in_const false (SOME false))
            (map_filter (fn ((_, loc'), th) =>
                            if loc' = loc then SOME (prop_of th) else NONE)
                        facts)
  else
    tab

fun consider_arities is_built_in_const th =
  let
    fun aux _ _ NONE = NONE
      | aux t args (SOME tab) =
        case t of
          t1 $ t2 => SOME tab |> aux t1 (t2 :: args) |> aux t2 []
        | Const (x as (s, _)) =>
          (if is_built_in_const x args |> fst then
             SOME tab
           else case Symtab.lookup tab s of
             NONE => SOME (Symtab.update (s, length args) tab)
           | SOME n => if n = length args then SOME tab else NONE)
        | _ => SOME tab
  in aux (prop_of th) [] end

(* FIXME: This is currently only useful for polymorphic type encodings. *)
fun could_benefit_from_ext is_built_in_const facts =
  fold (consider_arities is_built_in_const o snd) facts (SOME Symtab.empty)
  |> is_none

(* High enough so that it isn't wrongly considered as very relevant (e.g., for E
   weights), but low enough so that it is unlikely to be truncated away if few
   facts are included. *)
val special_fact_index = 75

fun relevance_filter ctxt threshold0 decay max_relevant is_built_in_const
        (fudge as {threshold_divisor, ridiculous_threshold, ...})
        ({add, del, ...} : relevance_override) facts chained_ts hyp_ts concl_t =
  let
    val thy = Proof_Context.theory_of ctxt
    val const_tab = fold (count_fact_consts thy fudge) facts Symtab.empty
    val add_pconsts = add_pconsts_in_term thy is_built_in_const false o SOME
    val chained_const_tab = Symtab.empty |> fold (add_pconsts true) chained_ts
    val goal_const_tab =
      Symtab.empty |> fold (add_pconsts true) hyp_ts
                   |> add_pconsts false concl_t
      |> (fn tab => if Symtab.is_empty tab then chained_const_tab else tab)
      |> fold (if_empty_replace_with_locality thy is_built_in_const facts)
              [Chained, Assum, Local]
    val add_ths = Attrib.eval_thms ctxt add
    val del_ths = Attrib.eval_thms ctxt del
    val facts = facts |> filter_out (member Thm.eq_thm_prop del_ths o snd)
    fun iter j remaining_max threshold rel_const_tab hopeless hopeful =
      let
        fun relevant [] _ [] =
            (* Nothing has been added this iteration. *)
            if j = 0 andalso threshold >= ridiculous_threshold then
              (* First iteration? Try again. *)
              iter 0 max_relevant (threshold / threshold_divisor) rel_const_tab
                   hopeless hopeful
            else
              []
          | relevant candidates rejects [] =
            let
              val (accepts, more_rejects) =
                take_most_relevant ctxt max_relevant remaining_max fudge
                                   candidates
              val rel_const_tab' =
                rel_const_tab
                |> fold (add_pconst_to_table false) (maps (snd o fst) accepts)
              fun is_dirty (c, _) =
                Symtab.lookup rel_const_tab' c <> Symtab.lookup rel_const_tab c
              val (hopeful_rejects, hopeless_rejects) =
                 (rejects @ hopeless, ([], []))
                 |-> fold (fn (ax as (_, consts), old_weight) =>
                              if exists is_dirty consts then
                                apfst (cons (ax, NONE))
                              else
                                apsnd (cons (ax, old_weight)))
                 |>> append (more_rejects
                             |> map (fn (ax as (_, consts), old_weight) =>
                                        (ax, if exists is_dirty consts then NONE
                                             else SOME old_weight)))
              val threshold =
                1.0 - (1.0 - threshold)
                      * Math.pow (decay, Real.fromInt (length accepts))
              val remaining_max = remaining_max - length accepts
            in
              trace_msg ctxt (fn () => "New or updated constants: " ^
                  commas (rel_const_tab' |> Symtab.dest
                          |> subtract (op =) (rel_const_tab |> Symtab.dest)
                          |> map string_for_hyper_pconst));
              map (fst o fst) accepts @
              (if remaining_max = 0 then
                 []
               else
                 iter (j + 1) remaining_max threshold rel_const_tab'
                      hopeless_rejects hopeful_rejects)
            end
          | relevant candidates rejects
                     (((ax as (((_, loc), _), fact_consts)), cached_weight)
                      :: hopeful) =
            let
              val weight =
                case cached_weight of
                  SOME w => w
                | NONE => fact_weight fudge loc const_tab rel_const_tab
                                      chained_const_tab fact_consts
            in
              if weight >= threshold then
                relevant ((ax, weight) :: candidates) rejects hopeful
              else
                relevant candidates ((ax, weight) :: rejects) hopeful
            end
        in
          trace_msg ctxt (fn () =>
              "ITERATION " ^ string_of_int j ^ ": current threshold: " ^
              Real.toString threshold ^ ", constants: " ^
              commas (rel_const_tab |> Symtab.dest
                      |> filter (curry (op <>) [] o snd)
                      |> map string_for_hyper_pconst));
          relevant [] [] hopeful
        end
    fun prepend_facts ths accepts =
      ((facts |> filter (member Thm.eq_thm_prop ths o snd)) @
       (accepts |> filter_out (member Thm.eq_thm_prop ths o snd)))
      |> take max_relevant
    fun uses_const s t =
      fold_aterms (curry (fn (Const (s', _), false) => s' = s | (_, b) => b)) t
                  false
    fun add_set_const_thms accepts (s, ths) =
      if exists (uses_const s o prop_of o snd) accepts orelse
         exists (uses_const s) (concl_t :: hyp_ts) then
        append ths
      else
        I
    fun insert_into_facts accepts [] = accepts
      | insert_into_facts accepts ths =
        let
          val add = facts |> filter (member Thm.eq_thm_prop ths o snd)
          val (bef, after) =
            accepts |> filter_out (member Thm.eq_thm_prop ths o snd)
                    |> take (max_relevant - length add)
                    |> chop special_fact_index
        in bef @ add @ after end
    fun insert_special_facts accepts =
       [] |> could_benefit_from_ext is_built_in_const accepts ? cons @{thm ext}
          |> fold (add_set_const_thms accepts) set_consts
          |> insert_into_facts accepts
  in
    facts |> map_filter (pair_consts_fact thy is_built_in_const fudge)
          |> iter 0 max_relevant threshold0 goal_const_tab []
          |> not (null add_ths) ? prepend_facts add_ths
          |> insert_special_facts
          |> tap (fn accepts => trace_msg ctxt (fn () =>
                      "Total relevant: " ^ string_of_int (length accepts)))
  end


(***************************************************************)
(* Retrieving and filtering lemmas                             *)
(***************************************************************)

(*** retrieve lemmas and filter them ***)

(*Reject theorems with names like "List.filter.filter_list_def" or
  "Accessible_Part.acc.defs", as these are definitions arising from packages.*)
fun is_package_def a =
  let val names = Long_Name.explode a in
    (length names > 2 andalso not (hd names = "local") andalso
     String.isSuffix "_def" a) orelse String.isSuffix "_defs" a
  end

fun uniquify xs =
  Termtab.fold (cons o snd)
               (fold (Termtab.update o `(prop_of o snd)) xs Termtab.empty) []

(* FIXME: put other record thms here, or declare as "no_atp" *)
fun multi_base_blacklist ctxt ho_atp =
  ["defs", "select_defs", "update_defs", "split", "splits", "split_asm",
   "cases", "ext_cases", "eq.simps", "eq.refl", "nchotomy", "case_cong",
   "weak_case_cong"]
  |> not (ho_atp orelse (Config.get ctxt instantiate_inducts)) ?
        append ["induct", "inducts"]
  |> map (prefix ".")

val max_lambda_nesting = 3 (*only applies if not ho_atp*)

fun term_has_too_many_lambdas max (t1 $ t2) =
    exists (term_has_too_many_lambdas max) [t1, t2]
  | term_has_too_many_lambdas max (Abs (_, _, t)) =
    max = 0 orelse term_has_too_many_lambdas (max - 1) t
  | term_has_too_many_lambdas _ _ = false

(* Don't count nested lambdas at the level of formulas, since they are
   quantifiers. *)
fun formula_has_too_many_lambdas true _ _ = false (*i.e. ho_atp*)
  | formula_has_too_many_lambdas _ Ts (Abs (_, T, t)) =
      formula_has_too_many_lambdas false (T :: Ts) t
  | formula_has_too_many_lambdas _ Ts t =
    if member (op =) [HOLogic.boolT, propT] (fastype_of1 (Ts, t)) then
      exists (formula_has_too_many_lambdas false Ts) (#2 (strip_comb t))
    else
      term_has_too_many_lambdas max_lambda_nesting t

(* The max apply depth of any "metis" call in "Metis_Examples" (on 2007-10-31)
   was 11. *)
val max_apply_depth = 15

fun apply_depth (f $ t) = Int.max (apply_depth f, apply_depth t + 1)
  | apply_depth (Abs (_, _, t)) = apply_depth t
  | apply_depth _ = 0

fun is_formula_too_complex ho_atp t =
  apply_depth t > max_apply_depth orelse formula_has_too_many_lambdas ho_atp [] t

(* FIXME: Extend to "Meson" and "Metis" *)
val exists_sledgehammer_const =
  exists_Const (fn (s, _) => String.isPrefix sledgehammer_prefix s)

(* FIXME: make more reliable *)
val exists_low_level_class_const =
  exists_Const (fn (s, _) =>
     String.isSubstring (Long_Name.separator ^ "class" ^ Long_Name.separator) s)

fun is_metastrange_theorem th =
  case head_of (concl_of th) of
    Const (s, _) => (s <> @{const_name Trueprop} andalso
                     s <> @{const_name "=="})
  | _ => false

fun is_that_fact th =
  String.isSuffix (Long_Name.separator ^ Obtain.thatN) (Thm.get_name_hint th)
  andalso exists_subterm (fn Free (s, _) => s = Name.skolem Auto_Bind.thesisN
                           | _ => false) (prop_of th)

(**** Predicates to detect unwanted facts (prolific or likely to cause
      unsoundness) ****)

fun is_theorem_bad_for_atps ho_atp exporter thm =
  is_metastrange_theorem thm orelse
  (not exporter andalso
   let val t = prop_of thm in
     is_formula_too_complex ho_atp t orelse exists_type type_has_top_sort t orelse
     exists_sledgehammer_const t orelse exists_low_level_class_const t orelse
     is_that_fact thm
   end)

fun meta_equify (@{const Trueprop}
                 $ (Const (@{const_name HOL.eq}, Type (_, [T, _])) $ t1 $ t2)) =
    Const (@{const_name "=="}, T --> T --> @{typ prop}) $ t1 $ t2
  | meta_equify t = t

val normalize_simp_prop =
  meta_equify
  #> map_aterms (fn Var ((s, _), T) => Var ((s, 0), T) | t => t)
  #> map_types (map_type_tvar (fn ((s, _), S) => TVar ((s, 0), S)))

fun clasimpset_rule_table_of ctxt =
  let
    fun add loc g f = fold (Termtab.update o rpair loc o g o prop_of o f)
    val {safeIs, safeEs, hazIs, hazEs, ...} = ctxt |> claset_of |> Classical.rep_cs
    val intros = Item_Net.content safeIs @ Item_Net.content hazIs
    val elims = map Classical.classical_rule (Item_Net.content safeEs @ Item_Net.content hazEs)
    val simps = ctxt |> simpset_of |> dest_ss |> #simps
  in
    Termtab.empty |> add Intro I I intros
                  |> add Elim I I elims
                  |> add Simp I snd simps
                  |> add Simp normalize_simp_prop snd simps
  end

fun all_facts ctxt ho_atp reserved exporter add_ths chained_ths =
  let
    val thy = Proof_Context.theory_of ctxt
    val global_facts = Global_Theory.facts_of thy
    val local_facts = Proof_Context.facts_of ctxt
    val named_locals = local_facts |> Facts.dest_static []
    val assms = Assumption.all_assms_of ctxt
    fun is_assum th = exists (fn ct => prop_of th aconv term_of ct) assms
    val is_chained = member Thm.eq_thm_prop chained_ths
    val clasimpset_table = clasimpset_rule_table_of ctxt
    fun locality_of_theorem global (name: string) th =
      if String.isSubstring ".induct" name orelse(*FIXME: use structured name*)
         String.isSubstring ".inducts" name then
           Induction
      else if is_chained th then
        Chained
      else if global then
        case Termtab.lookup clasimpset_table (prop_of th) of
          SOME loc => loc
        | NONE => General
      else if is_assum th then Assum else Local
    fun is_good_unnamed_local th =
      not (Thm.has_name_hint th) andalso
      forall (fn (_, ths) => not (member Thm.eq_thm_prop ths th)) named_locals
    val unnamed_locals =
      union Thm.eq_thm_prop (Facts.props local_facts) chained_ths
      |> filter is_good_unnamed_local |> map (pair "" o single)
    val full_space =
      Name_Space.merge (Facts.space_of global_facts, Facts.space_of local_facts)
    fun add_facts global foldx facts =
      foldx (fn (name0, ths) =>
        if not exporter andalso name0 <> "" andalso
           forall (not o member Thm.eq_thm_prop add_ths) ths andalso
           (Facts.is_concealed facts name0 orelse
            (not (Config.get ctxt ignore_no_atp) andalso
             is_package_def name0) orelse
            exists (fn s => String.isSuffix s name0)
                   (multi_base_blacklist ctxt ho_atp) orelse
            String.isSuffix "_def_raw" (* FIXME: crude hack *) name0) then
          I
        else
          let
            val multi = length ths > 1
            val backquote_thm =
              backquote o string_for_term ctxt o close_form o prop_of
            fun check_thms a =
              case try (Proof_Context.get_thms ctxt) a of
                NONE => false
              | SOME ths' => eq_list Thm.eq_thm_prop (ths, ths')
          in
            pair 1
            #> fold (fn th => fn (j, (multis, unis)) =>
                        (j + 1,
                         if not (member Thm.eq_thm_prop add_ths th) andalso
                            is_theorem_bad_for_atps ho_atp exporter th then
                           (multis, unis)
                         else
                           let
                             val new =
                               (((fn () =>
                                 if name0 = "" then
                                   th |> backquote_thm
                                 else
                                   [Facts.extern ctxt facts name0,
                                    Name_Space.extern ctxt full_space name0,
                                    name0]
                                   |> find_first check_thms
                                   |> (fn SOME name =>
                                          make_name reserved multi j name
                                        | NONE => "")),
                                locality_of_theorem global name0 th), th)
                           in
                             if multi then (new :: multis, unis)
                             else (multis, new :: unis)
                           end)) ths
            #> snd
          end)
  in
    (* The single-name theorems go after the multiple-name ones, so that single
       names are preferred when both are available. *)
    ([], []) |> add_facts false fold local_facts (unnamed_locals @ named_locals)
             |> add_facts true Facts.fold_static global_facts global_facts
             |> op @
  end

fun external_frees t =
  [] |> Term.add_frees t |> filter_out (can Name.dest_internal o fst)

fun nearly_all_facts ctxt ho_atp ({add, only, ...} : relevance_override)
                     chained_ths hyp_ts concl_t =
  let
    val thy = Proof_Context.theory_of ctxt
    val reserved = reserved_isar_keyword_table ()
    val add_ths = Attrib.eval_thms ctxt add
    val ind_stmt =
      Logic.list_implies (hyp_ts |> filter_out (null o external_frees), concl_t)
      |> Object_Logic.atomize_term thy
    val ind_stmt_xs = external_frees ind_stmt
  in
    (if only then
       maps (map (fn ((name, loc), th) => ((K name, loc), th))
             o fact_from_ref ctxt reserved chained_ths) add
     else
       all_facts ctxt ho_atp reserved false add_ths chained_ths)
    |> Config.get ctxt instantiate_inducts
       ? maps (instantiate_if_induct_rule ctxt ind_stmt ind_stmt_xs)
    |> (not (Config.get ctxt ignore_no_atp) andalso not only)
       ? filter_out (No_ATPs.member ctxt o snd)
    |> uniquify
  end

fun relevant_facts ctxt (threshold0, threshold1) max_relevant is_built_in_const
                   fudge (override as {only, ...}) chained_ths hyp_ts concl_t
                   facts =
  let
    val thy = Proof_Context.theory_of ctxt
    val decay = Math.pow ((1.0 - threshold1) / (1.0 - threshold0),
                          1.0 / Real.fromInt (max_relevant + 1))
  in
    trace_msg ctxt (fn () => "Considering " ^ string_of_int (length facts) ^
                             " facts");
    (if only orelse threshold1 < 0.0 then
       facts
     else if threshold0 > 1.0 orelse threshold0 > threshold1 orelse
             max_relevant = 0 then
       []
     else
       relevance_filter ctxt threshold0 decay max_relevant is_built_in_const
           fudge override facts (chained_ths |> map prop_of) hyp_ts
           (concl_t |> theory_constify fudge (Context.theory_name thy)))
    |> map (apfst (apfst (fn f => f ())))
  end

end;