(*  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_Problem_Generate.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_Problem_Generate

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 Logic.all_const) 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, 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)

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 x ts =

      let val (built_in, ts) = is_built_in_const x ts in

        (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 x ts

      | (Free x, ts) => do_const false 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 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}

          |> 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)

val crude_zero_vars =

  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

    val thy = Proof_Context.theory_of ctxt

    val atomize = HOLogic.mk_Trueprop o Object_Logic.atomize_term thy

    fun add loc g f =

      fold (Termtab.update o rpair loc o g o crude_zero_vars 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 =

      Item_Net.content safeEs @ Item_Net.content hazEs

      |> map Classical.classical_rule

    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 atomize 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 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;