(* File: Weight.v  (last edited on 27/10/2000) (c) Klaus Weich  *)
Fixpoint weight (a : form) : nat :=
match a with
| Falsum => 1
| Atom _ => 1
| AndF a b => S (weight a + weight b)
| OrF Falsum b => S (weight b)
| OrF (Atom _) b => S (weight b)
| OrF a b => S (S (weight b + weight a))
| Imp a b => weight_neg a + weight b
end
with weight_neg (a : form) : nat :=
match a with
| Falsum => 0
| Atom _ => 0
| AndF a b => S (weight_neg a + weight_neg b)
| OrF a b => S (S (S (weight_neg a + weight_neg b)))
| Imp Falsum b => 1
| Imp (Atom _) Falsum => 2
| Imp (Atom _) (Atom _) => 1
| Imp (Atom _) b => S (S (S (weight_neg b)))
| Imp a b => S (S (S (S (weight_neg b + weight a))))
end.
Fixpoint weight_goal (a : form) : nat :=
match a with
| Falsum => 0
| Atom _ => 0
| AndF _ _ => 1
| OrF _ _ => 1
| Imp _ b => S (weight_goal b)
end.
Definition weight_gamma :=
fold_right (fun (a : form) (n : nat) => weight a + n) 0.
(**********************************************************************)
intros a; elim a; clear a.
trivial.
trivial.
intros; simpl in |- *.
apply le_n_S.
apply le_O_n.
intros a ih_a b ih_b.
clear ih_a ih_b.
case a; clear a; intros; simpl in |- *; apply le_n_S; apply le_O_n.
intros a ih_a b ih_b.
simpl in |- *.
fold weight_neg in |- *.
apply le_trans with (weight b); try assumption.
apply (plus_le_compat_r 0 (weight_neg a) (weight b)).
apply le_O_n.
Qed.
intros j a; case a; clear a.
apply le_n_Sn.
intros; apply le_trans with 2; apply le_n_Sn.
intros; apply le_n.
intros; apply le_n.
intros; apply le_n.
Qed.
intros l.
elim l; clear l.
intro a; trivial.
intros i l ih a.
simpl in |- *.
apply ih with (a := Imp (Atom i) a).
Qed.

Lemma weight_gamma_weak :
forall (a b : form) (gamma : flist) (n : nat),
weight a < weight b ->
weight_gamma (b :: gamma) < S n -> weight_gamma (a :: gamma) < n.