Definition model := list (var * expr).Inductive superposition_result : Type :=
| Valid : superposition_result
| C_example : model -> M.t -> superposition_result
| Aborted : list clause -> superposition_result.Inductive superposition_result : Type :=
| Valid : superposition_result
| C_example : model -> M.t -> superposition_result
| Aborted : list clause -> superposition_result.Inductive superposition_result : Type :=
| Valid : superposition_result
| C_example : model -> M.t -> superposition_result
| Aborted : list clause -> superposition_result.Inductive superposition_result : Type :=
| Valid : superposition_result
| C_example : model -> M.t -> superposition_result
| Aborted : list clause -> superposition_result.(* side condition used in superposition rules below *)
(* begin hide *)
Definition pure_atom_gt1 a (l: list pure_atom) :=
  match l with b :: _ => pure_atom_gt a b | _ => true end.(* end hide *)

(** ef:
Equality factoring *)

Fixpoint ef_aux neg u0 u v pos0 pos l0 : list clause :=
  match pos with
  | (Eqv s t as a2) :: pos' =>
    if expr_eq s u && greater_than_all u0 neg
    then mkPureClause
           (insu_atm (norm_pure_atom (Eqv v t)) neg)
           (insu_atm (norm_pure_atom (Eqv u t))
                 (merge pure_atom_cmp (List.rev pos0) pos)) ::
             ef_aux neg u0 u v (insu_atm a2 pos0) pos' l0
    else l0
  | nil => l0
  end.Definition ef (cty : ce_type) (c : clause) l0 : list clause :=
  match cty, c with
  | CexpEf, PureClause neg (Eqv (Var u0 as u) v :: pos) _ _ =>
    if greater_than_all u0 neg then ef_aux neg u0 u v nil pos l0
    else l0
  | _, _ => l0
  end.(** sp:
left and right superposition *)

Definition sp (cty : ce_type) (c d : clause) l0 : list clause :=
  match cty, c, d with
  (* negative (left) superposition *)
  | CexpL, PureClause (Eqv s' v :: neg') pos' _ _,
           PureClause neg (Eqv (Var s0 as s) t :: pos) _ _ =>
    if expr_eq s s' && expr_lt t s && expr_lt v s' &&
       pure_atom_gt1 (Eqv s t) pos && greater_than_all s0 neg
    then mkPureClause
      (insu_atm (norm_pure_atom (Eqv t v)) (merge pure_atom_cmp neg neg'))
      (merge pure_atom_cmp pos pos') :: l0
    else l0
  (* positive (right) superposition *)
  | CexpR, PureClause neg (Eqv (Var s0 as s) t :: pos) _ _,
           PureClause neg' (Eqv (Var s'0 as s') v :: pos') _ _ =>
    if expr_eq s s' && expr_lt t s && expr_lt v s' &&
       pure_atom_gt1 (Eqv s t) pos && pure_atom_gt1 (Eqv s' v) pos' &&
       pure_atom_gt (Eqv s t) (Eqv s' v) &&
       greater_than_all s0 neg && greater_than_all s'0 neg'
    then mkPureClause
      (merge pure_atom_cmp neg neg')
      (insu_atm (norm_pure_atom (Eqv t v)) (merge pure_atom_cmp pos pos')) :: l0
    else l0
  | _, _, _ => l0
  end.(** Retractive rules:
    -demodulation (simplification by positive unit clauses),
    -equality resolution *)

(* u[s->t] *)
Definition rewrite_expr s t u := if expr_eq s u then t else u.Definition rewrite_by s t atm :=
  match atm with Eqv u v =>
    if expr_eq s u then if expr_eq s v then norm_pure_atom (Eqv t t)
                        else norm_pure_atom (Eqv t v)
    else if expr_eq s v then norm_pure_atom (Eqv u t)
         else atm
  end.Definition rewrite_in_space s t atm :=
  match atm with
  | Next u v => Next (rewrite_expr s t u) (rewrite_expr s t v)
  | Lseg u v => Lseg (rewrite_expr s t u) (rewrite_expr s t v)
  end.(** Delete resolved negative atoms, i.e., atoms of the form [Eqv x x]
    lying in negative positions.  This is called equality resolution by some. *)

Definition delete_resolved (c : clause) : clause :=
  match c with
  | PureClause neg pos _ _ =>
     mkPureClause (sortu_atms (remove_trivial_atoms neg)) (sortu_atms pos)
  | _ => c
(*  | _ => mkPureClause nil [Eqv Nil Nil] (* impossible *)*)
  end.(** Filter tautological clauses *)

Definition not_taut (c: clause) :=
  negb (match c with
        | PureClause neg pos _ _ =>
          existsb (fun a => existsb (fun b =>
                     pure_atom_eq a b) pos) neg ||
          existsb (fun a =>
            match a with Eqv e1 e2 => expr_eq e1 e2 end) pos
        | _ => false end).(** Rewrite [c] by positive unit clauses in [l]. Delete resolved atoms
    from the resulting clause. Argument [l] is already sorted so no need to
    re-sort. *)

Definition simplify (l : list clause) (c : clause) : clause :=
  delete_resolved (fold_left (fun d c => demodulate c d) l c).Definition simplify_atoms (l : list clause) (atms : list space_atom)
  : list space_atom :=
  fold_left (fun atms d => map (rewrite_clause_in_space d) atms) l atms.(** Derive clauses from clause [c] and clauses [l] using [cty] inferences alone.
    Forward-simplify any resulting clauses using facts in [l] (note: we do no
    backward simplification here since this would greatly complicate the termination
    proof). *)

Definition infer (cty : ce_type) (c : clause) (l : list clause) : list clause :=
  print_inferred_list (rsort_uniq compare_clause
    (filter not_taut (map (simplify nil)
      (ef cty c (fold_left (fun l0 d => sp cty c d l0) l nil))))).(** Model generation: build a candidate model for clauses [l] *)

Definition apply_model (R : model) (cl : clause) : clause :=
  fold_right (fun ve => subst_clause (fst ve) (snd ve)) cl R.Definition is_model_of (R : model) (gamma delta : list pure_atom) : bool :=
  match fold_right (fun ve => subst_pures_delete (fst ve) (snd ve))
               (remove_trivial_atoms gamma) R,
          fold_right (fun ve => subst_pures (fst ve) (snd ve)) delta R with
  | _::_, _ => true
  | nil , delta' => negb (forallb nonreflex_atom delta')
  end.(** Check whether R is a model of [Pi+ /\ Pi-]; used in the Veristar main loop *)

Definition is_model_of_PI (R: model) (nc : (*negative spatial*) clause) : bool :=
 match nc with NegSpaceClause pi_plus _ pi_minus =>
  match fold_right (fun ve =>
          subst_pures_delete (fst ve) (snd ve)) (remove_trivial_atoms pi_plus) R,
        fold_right (fun ve =>
          subst_pures (fst ve) (snd ve)) pi_minus R with
  | nil , pi_minus' => forallb nonreflex_atom pi_minus'
  | _ :: _ , _ => false
  end
 | _ => false
 end.(** Is there a rewrite rule [v'->r] in [R] s.t. [v==v']? *)

Definition reduces (R: model) (v : var) :=
  existsb (fun ve' => if Ident.eq_dec v (fst ve') then true else false) R.(** Does clause [cl] generate a new rewrite rule that must be added to the
    candidate model [R]? If so, return the rewrite rule paired with [cl]. Otherwise
    [cl] is a c-example for the current candidate model (invariant: [clause_generate
    R cl] is only called when [R] is [not] already a model for [cl]) so determine which
    type of c-example [cl] is, and return that as a value of [ce_type]. *)

Definition clause_generate (R : model) (cl : clause)
  : (var * expr * clause) + ce_type :=
  match cl with
  | PureClause gamma (Eqv (Var l' as l) r :: delta) _ _ as c' =>
      if greater_than_expr l' r && greater_than_all l' gamma &&
         greater_than_atoms (Eqv l r) delta
      then if reduces R l' then inr _ CexpR
           else if is_model_of (List.rev R) nil (map (rewrite_by l r) delta)
                then inr _ CexpEf else inl _ (l', r, cl)
      else inr _ CexpL
  | _ => inr _ CexpL
  end.(** Construct a candidate model for [l] or fail with (1) the partial model built
    so far (for debugging); (2) the clause that failed; and (3) its [ce_type]. *)

Fixpoint partial_mod (R : model) (acc l : list clause)
  : (model * list clause) + (model * clause * ce_type) :=
  match l with
  | nil => inl _ (R, acc)
  | (PureClause gamma delta _ _) as cl :: l' =>
      if is_model_of (List.rev R) gamma delta then partial_mod R acc l'
      else match clause_generate R cl with
           | (inl (v, exp, cl')) => partial_mod ((v, exp) :: R) (cl' :: acc) l'
           | (inr cty) => inr _ (print_ce_clause R cl cty)
           end
  | _ => inl _ (R, acc)
  end.Definition is_empty_clause (cl : clause) :=
  match cl with PureClause nil nil _ _ => true | _ => false end.Definition is_unit_clause (cl : clause) :=
  match cl with PureClause nil (a :: nil) _ _ => true | _ => false end.

Lemma Ppred_decrease n : (n<>1)%positive -> (nat_of_P (Ppred n)<nat_of_P n)%nat.