intros p q n Hle; simpl in |- *.
rewrite <- (plus_n_Sm p q).
rewrite <- (minus_Sn_m (p + q) q).
rewrite (plus_comm p); rewrite minus_plus; auto with *.
auto with arith.
Qed.

(* Specifications: *)
Theorem Qpositive_c_unfold2 :
forall p q n : nat,
S p + (S p + S q) <= S n ->
Qpositive_c (S p) (S p + S q) (S n) = dL (Qpositive_c (S p) (S q) n).