(*  Title:      HOL/Tools/Sledgehammer/sledgehammer_fact_filter.ML

    Author:     Jia Meng, Cambridge University Computer Laboratory and NICTA

    Author:     Jasmin Blanchette, TU Muenchen

*)

signature SLEDGEHAMMER_FACT_FILTER =

sig

  type relevance_override =

    {add: Facts.ref list,

     del: Facts.ref list,

     only: bool}

  val trace : bool Unsynchronized.ref

  val name_thm_pairs_from_ref :

    Proof.context -> unit Symtab.table -> thm list -> Facts.ref

    -> ((unit -> string * bool) * (bool * thm)) list

  val relevant_facts :

    bool -> real -> real option -> int -> bool -> relevance_override

    -> Proof.context * (thm list * 'a) -> term list -> term

    -> ((string * bool) * thm) list

end;

structure Sledgehammer_Fact_Filter : SLEDGEHAMMER_FACT_FILTER =

struct

open Sledgehammer_Util

val trace = Unsynchronized.ref false

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

val respect_no_atp = true

type relevance_override =

  {add: Facts.ref list,

   del: Facts.ref list,

   only: bool}

val sledgehammer_prefix = "Sledgehammer" ^ Long_Name.separator

fun repair_name reserved multi j name =

  (name |> Symtab.defined reserved name ? quote) ^

  (if multi then "(" ^ Int.toString j ^ ")" else "")

fun name_thm_pairs_from_ref ctxt reserved chained_ths xref =

  let

    val ths = ProofContext.get_fact ctxt xref

    val name = Facts.string_of_ref xref

    val multi = length ths > 1

  in

    fold (fn th => fn (j, rest) =>

             (j + 1, (fn () => (repair_name reserved multi j name,

                                member Thm.eq_thm chained_ths th),

                      (multi, th)) :: rest))

         ths (1, [])

    |> snd

  end

(***************************************************************)

(* Relevance Filtering                                         *)

(***************************************************************)

(*** constants with types ***)

(*An abstraction of Isabelle types*)

datatype pseudotype = PVar | PType of string * pseudotype list

fun string_for_pseudotype PVar = "?"

  | string_for_pseudotype (PType (s, Ts)) =

    (case Ts of

       [] => ""

     | [T] => string_for_pseudotype T

     | Ts => string_for_pseudotypes Ts ^ " ") ^ s

and string_for_pseudotypes Ts =

  "(" ^ commas (map string_for_pseudotype Ts) ^ ")"

(*Is the second type an instance of the first one?*)

fun match_pseudotype (PType (a, T), PType (b, U)) =

    a = b andalso match_pseudotypes (T, U)

  | match_pseudotype (PVar, _) = true

  | match_pseudotype (_, PVar) = false

and match_pseudotypes ([], []) = true

  | match_pseudotypes (T :: Ts, U :: Us) =

    match_pseudotype (T, U) andalso match_pseudotypes (Ts, Us)

(*Is there a unifiable constant?*)

fun pseudoconst_mem f const_tab (c, c_typ) =

  exists (curry (match_pseudotypes o f) c_typ)

         (these (Symtab.lookup const_tab c))

fun pseudotype_for (Type (c,typs)) = PType (c, map pseudotype_for typs)

  | pseudotype_for (TFree _) = PVar

  | pseudotype_for (TVar _) = PVar

(* Pairs a constant with the list of its type instantiations. *)

fun pseudoconst_for thy (c, T) =

  (c, map pseudotype_for (Sign.const_typargs thy (c, T)))

  handle TYPE _ => (c, [])  (* Variable (locale constant): monomorphic *)

fun string_for_pseudoconst (s, []) = s

  | string_for_pseudoconst (s, Ts) = s ^ string_for_pseudotypes Ts

fun string_for_super_pseudoconst (s, [[]]) = s

  | string_for_super_pseudoconst (s, Tss) =

    s ^ "{" ^ commas (map string_for_pseudotypes Tss) ^ "}"

(*Add a const/type pair to the table, but a [] entry means a standard connective,

  which we ignore.*)

fun add_const_to_table (c, ctyps) =

  Symtab.map_default (c, [ctyps])

                     (fn [] => [] | ctypss => insert (op =) ctyps ctypss)

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

val fresh_prefix = "Sledgehammer.skolem."

val flip = Option.map not

(* These are typically simplified away by "Meson.presimplify". *)

val boring_consts =

  [@{const_name False}, @{const_name True}, @{const_name If}, @{const_name Let}]

fun get_consts thy pos ts =

  let

    (* We include free variables, as well as constants, to handle locales. For

       each quantifiers that must necessarily be skolemized by the ATP, we

       introduce a fresh constant to simulate the effect of Skolemization. *)

    fun do_term t =

      case t of

        Const x => add_const_to_table (pseudoconst_for thy x)

      | Free (s, _) => add_const_to_table (s, [])

      | t1 $ t2 => fold do_term [t1, t2]

      | Abs (_, _, t') => do_term t'

      | _ => I

    fun do_quantifier will_surely_be_skolemized body_t =

      do_formula pos body_t

      #> (if will_surely_be_skolemized then

            add_const_to_table (gensym fresh_prefix, [])

          else

            I)

    and do_term_or_formula T =

      if is_formula_type T then do_formula NONE else do_term

    and do_formula pos t =

      case t of

        Const (@{const_name all}, _) $ Abs (_, _, body_t) =>

        do_quantifier (pos = SOME false) body_t

      | @{const "==>"} $ t1 $ t2 =>

        do_formula (flip pos) t1 #> do_formula pos t2

      | Const (@{const_name "=="}, Type (_, [T, _])) $ t1 $ t2 =>

        fold (do_term_or_formula T) [t1, t2]

      | @{const Trueprop} $ t1 => do_formula pos t1

      | @{const Not} $ t1 => do_formula (flip pos) t1

      | Const (@{const_name All}, _) $ Abs (_, _, body_t) =>

        do_quantifier (pos = SOME false) body_t

      | Const (@{const_name Ex}, _) $ Abs (_, _, body_t) =>

        do_quantifier (pos = SOME true) body_t

      | @{const "op &"} $ t1 $ t2 => fold (do_formula pos) [t1, t2]

      | @{const "op |"} $ t1 $ t2 => fold (do_formula pos) [t1, t2]

      | @{const "op -->"} $ t1 $ t2 =>

        do_formula (flip pos) t1 #> do_formula pos t2

      | Const (@{const_name "op ="}, Type (_, [T, _])) $ t1 $ t2 =>

        fold (do_term_or_formula T) [t1, t2]

      | Const (@{const_name If}, Type (_, [_, Type (_, [T, _])]))

        $ t1 $ t2 $ t3 =>

        do_formula NONE t1 #> fold (do_term_or_formula T) [t2, t3]

      | Const (@{const_name Ex1}, _) $ Abs (_, _, body_t) =>

        do_quantifier (is_some pos) body_t

      | Const (@{const_name Ball}, _) $ t1 $ Abs (_, _, body_t) =>

        do_quantifier (pos = SOME false)

                      (HOLogic.mk_imp (incr_boundvars 1 t1 $ Bound 0, body_t))

      | Const (@{const_name Bex}, _) $ t1 $ Abs (_, _, body_t) =>

        do_quantifier (pos = SOME true)

                      (HOLogic.mk_conj (incr_boundvars 1 t1 $ Bound 0, body_t))

      | (t0 as Const (_, @{typ bool})) $ t1 =>

        do_term t0 #> do_formula pos t1  (* theory constant *)

      | _ => do_term t

  in

    Symtab.empty |> fold (Symtab.update o rpair []) boring_consts

                 |> fold (do_formula pos) ts

  end

(*Inserts a dummy "constant" referring to the theory name, so that relevance

  takes the given theory into account.*)

fun theory_const_prop_of theory_relevant th =

  if theory_relevant then

    let

      val name = Context.theory_name (theory_of_thm th)

      val t = Const (name ^ ". 1", @{typ bool})

    in t $ prop_of th end

  else

    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 "pseudotype list". *)

fun pseudotype_ord p =

  case p of

    (PVar, PVar) => EQUAL

  | (PVar, PType _) => LESS

  | (PType _, PVar) => GREATER

  | (PType q1, PType q2) =>

    prod_ord fast_string_ord (dict_ord pseudotype_ord) (q1, q2)

structure CTtab =

  Table(type key = pseudotype list val ord = dict_ord pseudotype_ord)

fun count_axiom_consts theory_relevant thy (_, th) =

  let

    fun do_const (a, T) =

      let val (c, cts) = pseudoconst_for thy (a, T) in

        (* Two-dimensional table update. Constant maps to types maps to

           count. *)

        CTtab.map_default (cts, 0) (Integer.add 1)

        |> Symtab.map_default (c, CTtab.empty)

      end

    fun do_term (Const x) = do_const x

      | do_term (Free x) = do_const x

      | do_term (t $ u) = do_term t #> do_term u

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

      | do_term _ = I

  in th |> theory_const_prop_of theory_relevant |> do_term end

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

(*The frequency of a constant is the sum of those of all instances of its type.*)

fun pseudoconst_freq match const_tab (c, cts) =

  CTtab.fold (fn (cts', m) => match (cts, cts') ? Integer.add m)

             (the (Symtab.lookup const_tab c)) 0

  handle Option.Option => 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. *)

fun rel_log (x : real) = 1.0 + 2.0 / Math.ln (x + 1.0)

fun irrel_log (x : real) = Math.ln (x + 19.0) / 6.4

(* Computes a constant's weight, as determined by its frequency. *)

val rel_weight = rel_log o real oo pseudoconst_freq match_pseudotypes

val irrel_weight =

  irrel_log o real oo pseudoconst_freq (match_pseudotypes o swap)

(* fun irrel_weight _ _ = 1.0  FIXME: OLD CODE *)

fun axiom_weight const_tab relevant_consts axiom_consts =

  case axiom_consts |> List.partition (pseudoconst_mem I relevant_consts)

                    ||> filter_out (pseudoconst_mem swap relevant_consts) of

    ([], []) => 0.0

  | (_, []) => 1.0

  | (rel, irrel) =>

    let

      val rel_weight = fold (curry Real.+ o rel_weight const_tab) rel 0.0

      val irrel_weight = fold (curry Real.+ o irrel_weight const_tab) irrel 0.0

      val res = rel_weight / (rel_weight + irrel_weight)

    in if Real.isFinite res then res else 0.0 end

fun consts_of_term thy t =

  Symtab.fold (fn (x, ys) => fold (fn y => cons (x, y)) ys)

              (get_consts thy (SOME true) [t]) []

fun pair_consts_axiom theory_relevant thy axiom =

  (axiom, axiom |> snd |> theory_const_prop_of theory_relevant

                |> consts_of_term thy)

type annotated_thm =

  ((unit -> string * bool) * thm) * (string * pseudotype list) list

fun rev_compare_pairs ((_, w1), (_, w2)) = Real.compare (w2, w1)

fun take_best max (new_pairs : (annotated_thm * real) list) =

  let

    val ((perfect, more_perfect), imperfect) =

      new_pairs |> List.partition (fn (_, w) => w > 0.99999)

                |>> chop (max - 1) ||> sort rev_compare_pairs

    val (accepted, rejected) =

      case more_perfect @ imperfect of

        [] => (perfect, [])

      | (q :: qs) => (q :: perfect, qs)

  in

    trace_msg (fn () => "Number of candidates: " ^

                        string_of_int (length new_pairs));

    trace_msg (fn () => "Effective threshold: " ^

                        Real.toString (#2 (hd accepted)));

    trace_msg (fn () => "Actually passed: " ^

        (accepted |> map (fn (((name, _), _), weight) =>

                             fst (name ()) ^ " [" ^ Real.toString weight ^ "]")

                  |> commas));

    (map #1 accepted, rejected)

  end

val threshold_divisor = 2.0

val ridiculous_threshold = 0.1

fun relevance_filter ctxt relevance_threshold relevance_decay max_relevant

                     theory_relevant ({add, del, ...} : relevance_override)

                     axioms goal_ts =

  let

    val thy = ProofContext.theory_of ctxt

    val const_tab = fold (count_axiom_consts theory_relevant thy) axioms

                         Symtab.empty

    val add_thms = maps (ProofContext.get_fact ctxt) add

    val del_thms = maps (ProofContext.get_fact ctxt) del

    fun iter j max threshold rel_const_tab rest =

      let

        fun game_over rejects =

          if j = 0 andalso threshold >= ridiculous_threshold then

            (* First iteration? Try again. *)

            iter 0 max (threshold / threshold_divisor) rel_const_tab rejects

          else

            (* Add "add:" facts. *)

            if null add_thms then

              []

            else

              map_filter (fn ((p as (_, th), _), _) =>

                             if member Thm.eq_thm add_thms th then SOME p

                             else NONE) rejects

        fun relevant ([], rejects) [] =

            (* Nothing has been added this iteration. *)

            game_over (map (apsnd SOME) rejects)

          | relevant (new_pairs, rejects) [] =

            let

              val (new_rels, more_rejects) = take_best max new_pairs

              val rel_const_tab' =

                rel_const_tab |> fold add_const_to_table (maps snd new_rels)

              fun is_dirty (c, _) =

                Symtab.lookup rel_const_tab' c <> Symtab.lookup rel_const_tab c

              val rejects =

                more_rejects @ rejects

                |> map (fn (ax as (_, consts), old_weight) =>

                           (ax, if exists is_dirty consts then NONE

                                else SOME old_weight))

              val threshold = threshold + (1.0 - threshold) * relevance_decay

              val max = max - length new_rels

            in

              trace_msg (fn () => "New or updated constants: " ^

                  commas (rel_const_tab' |> Symtab.dest

                          |> subtract (op =) (Symtab.dest rel_const_tab)

                          |> map string_for_super_pseudoconst));

              map #1 new_rels @

              (if max = 0 then game_over rejects

               else iter (j + 1) max threshold rel_const_tab' rejects)

            end

          | relevant (new_rels, rejects)

                     (((ax as ((name, th), axiom_consts)), cached_weight)

                      :: rest) =

            let

              val weight =

                case cached_weight of

                  SOME w => w

                | NONE => axiom_weight const_tab rel_const_tab axiom_consts

            in

              if weight >= threshold then

                relevant ((ax, weight) :: new_rels, rejects) rest

              else

                relevant (new_rels, (ax, weight) :: rejects) rest

            end

        in

          trace_msg (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_super_pseudoconst));

          relevant ([], []) rest

        end

  in

    axioms |> filter_out (member Thm.eq_thm del_thms o snd)

           |> map (rpair NONE o pair_consts_axiom theory_relevant thy)

           |> iter 0 max_relevant relevance_threshold

                   (get_consts thy (SOME false) goal_ts)

           |> tap (fn res => trace_msg (fn () =>

                                "Total relevant: " ^ Int.toString (length res)))

  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 make_fact_table xs =

  fold (Termtab.update o `(prop_of o snd)) xs Termtab.empty

fun make_unique xs = Termtab.fold (cons o snd) (make_fact_table xs) []

(* FIXME: put other record thms here, or declare as "no_atp" *)

val multi_base_blacklist =

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

   "split_asm", "cases", "ext_cases", "eq.simps", "eq.refl", "nchotomy",

   "case_cong", "weak_case_cong"]

  |> map (prefix ".")

val max_lambda_nesting = 3

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 Ts (Abs (_, T, t)) =

    formula_has_too_many_lambdas (T :: Ts) t

  | formula_has_too_many_lambdas Ts t =

    if is_formula_type (fastype_of1 (Ts, t)) then

      exists (formula_has_too_many_lambdas 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 t =

  apply_depth t > max_apply_depth orelse formula_has_too_many_lambdas [] t

val exists_sledgehammer_const =

  exists_Const (fn (s, _) => String.isPrefix sledgehammer_prefix s)

fun is_strange_theorem th =

  case head_of (concl_of th) of

      Const (a, _) => (a <> @{const_name Trueprop} andalso

                       a <> @{const_name "=="})

    | _ => false

val type_has_top_sort =

  exists_subtype (fn TFree (_, []) => true | TVar (_, []) => true | _ => false)

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

      unsoundness) ****)

(* Too general means, positive equality literal with a variable X as one

   operand, when X does not occur properly in the other operand. This rules out

   clearly inconsistent facts such as X = a | X = b, though it by no means

   guarantees soundness. *)

(* Unwanted equalities are those between a (bound or schematic) variable that

   does not properly occur in the second operand. *)

val is_exhaustive_finite =

  let

    fun is_bad_equal (Var z) t =

        not (exists_subterm (fn Var z' => z = z' | _ => false) t)

      | is_bad_equal (Bound j) t = not (loose_bvar1 (t, j))

      | is_bad_equal _ _ = false

    fun do_equals t1 t2 = is_bad_equal t1 t2 orelse is_bad_equal t2 t1

    fun do_formula pos t =

      case (pos, t) of

        (_, @{const Trueprop} $ t1) => do_formula pos t1

      | (true, Const (@{const_name all}, _) $ Abs (_, _, t')) =>

        do_formula pos t'

      | (true, Const (@{const_name All}, _) $ Abs (_, _, t')) =>

        do_formula pos t'

      | (false, Const (@{const_name Ex}, _) $ Abs (_, _, t')) =>

        do_formula pos t'

      | (_, @{const "==>"} $ t1 $ t2) =>

        do_formula (not pos) t1 andalso

        (t2 = @{prop False} orelse do_formula pos t2)

      | (_, @{const "op -->"} $ t1 $ t2) =>

        do_formula (not pos) t1 andalso

        (t2 = @{const False} orelse do_formula pos t2)

      | (_, @{const Not} $ t1) => do_formula (not pos) t1

      | (true, @{const "op |"} $ t1 $ t2) => forall (do_formula pos) [t1, t2]

      | (false, @{const "op &"} $ t1 $ t2) => forall (do_formula pos) [t1, t2]

      | (true, Const (@{const_name "op ="}, _) $ t1 $ t2) => do_equals t1 t2

      | (true, Const (@{const_name "=="}, _) $ t1 $ t2) => do_equals t1 t2

      | _ => false

  in do_formula true end

fun has_bound_or_var_of_type tycons =

  exists_subterm (fn Var (_, Type (s, _)) => member (op =) tycons s

                   | Abs (_, Type (s, _), _) => member (op =) tycons s

                   | _ => false)

(* Facts are forbidden to contain variables of these types. The typical reason

   is that they lead to unsoundness. Note that "unit" satisfies numerous

   equations like "?x = ()". The resulting clauses will have no type constraint,

   yielding false proofs. Even "bool" leads to many unsound proofs, though only

   for higher-order problems. *)

val dangerous_types = [@{type_name unit}, @{type_name bool}, @{type_name prop}];

(* Facts containing variables of type "unit" or "bool" or of the form

   "ALL x. x = A | x = B | x = C" are likely to lead to unsound proofs if types

   are omitted. *)

fun is_dangerous_term full_types t =

  not full_types andalso

  let val t = transform_elim_term t in

    has_bound_or_var_of_type dangerous_types t orelse

    is_exhaustive_finite t

  end

fun is_theorem_bad_for_atps full_types thm =

  let val t = prop_of thm in

    is_formula_too_complex t orelse exists_type type_has_top_sort t orelse

    is_dangerous_term full_types t orelse exists_sledgehammer_const t orelse

    is_strange_theorem thm

  end

fun all_name_thms_pairs ctxt reserved full_types add_thms chained_ths =

  let

    val is_chained = member Thm.eq_thm chained_ths

    val global_facts = PureThy.facts_of (ProofContext.theory_of ctxt)

    val local_facts = ProofContext.facts_of ctxt

    val named_locals = local_facts |> Facts.dest_static []

    (* Unnamed, not chained formulas with schematic variables are omitted,

       because they are rejected by the backticks (`...`) parser for some

       reason. *)

    fun is_good_unnamed_local th =

      forall (fn (_, ths) => not (member Thm.eq_thm ths th)) named_locals

      andalso (not (exists_subterm is_Var (prop_of th)) orelse (is_chained th))

    val unnamed_locals =

      local_facts |> Facts.props |> 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_valid_facts foldx facts =

      foldx (fn (name0, ths) =>

        if name0 <> "" andalso

           forall (not o member Thm.eq_thm add_thms) ths andalso

           (Facts.is_concealed facts name0 orelse

            (respect_no_atp andalso is_package_def name0) orelse

            exists (fn s => String.isSuffix s name0) multi_base_blacklist orelse

            String.isSuffix "_def_raw" (* FIXME: crude hack *) name0) then

          I

        else

          let

            val multi = length ths > 1

            fun backquotify th =

              "`" ^ Print_Mode.setmp [Print_Mode.input]

                                 (Syntax.string_of_term ctxt) (prop_of th) ^ "`"

              |> String.translate (fn c => if Char.isPrint c then str c else "")

              |> simplify_spaces

            fun check_thms a =

              case try (ProofContext.get_thms ctxt) a of

                NONE => false

              | SOME ths' => Thm.eq_thms (ths, ths')

          in

            pair 1

            #> fold (fn th => fn (j, rest) =>

                 (j + 1,

                  if is_theorem_bad_for_atps full_types th andalso

                     not (member Thm.eq_thm add_thms th) then

                    rest

                  else

                    (fn () =>

                        (if name0 = "" then

                           th |> backquotify

                         else

                           let

                             val name1 = Facts.extern facts name0

                             val name2 = Name_Space.extern full_space name0

                           in

                             case find_first check_thms [name1, name2, name0] of

                               SOME name => repair_name reserved multi j name

                             | NONE => ""

                           end, is_chained th), (multi, th)) :: rest)) ths

            #> snd

          end)

  in

    [] |> add_valid_facts fold local_facts (unnamed_locals @ named_locals)

       |> add_valid_facts Facts.fold_static global_facts global_facts

  end

(* The single-name theorems go after the multiple-name ones, so that single

   names are preferred when both are available. *)

fun name_thm_pairs ctxt respect_no_atp =

  List.partition (fst o snd) #> op @ #> map (apsnd snd)

  #> respect_no_atp ? filter_out (No_ATPs.member ctxt o snd)

(***************************************************************)

(* ATP invocation methods setup                                *)

(***************************************************************)

fun relevant_facts full_types relevance_threshold relevance_decay max_relevant

                   theory_relevant (relevance_override as {add, del, only})

                   (ctxt, (chained_ths, _)) hyp_ts concl_t =

  let

    val relevance_decay =

      case relevance_decay of

        SOME x => x

      | NONE => 0.35 / Math.ln (Real.fromInt (max_relevant + 1))

    val add_thms = maps (ProofContext.get_fact ctxt) add

    val reserved = reserved_isar_keyword_table ()

    val axioms =

      (if only then

         maps (name_thm_pairs_from_ref ctxt reserved chained_ths) add

       else

         all_name_thms_pairs ctxt reserved full_types add_thms chained_ths)

      |> name_thm_pairs ctxt (respect_no_atp andalso not only)

      |> make_unique

  in

    trace_msg (fn () => "Considering " ^ Int.toString (length axioms) ^

                        " theorems");

    (if relevance_threshold > 1.0 then

       []

     else if relevance_threshold < 0.0 then

       axioms

     else

       relevance_filter ctxt relevance_threshold relevance_decay max_relevant

                        theory_relevant relevance_override axioms

                                        (concl_t :: hyp_ts))

    |> map (apfst (fn f => f ())) |> sort_wrt (fst o fst)

  end

end;