let T_local :=
(intros w'; simpl in |- *; case (Qpositive_i w'); intros p' q' Hrec p q Heq;
rewrite (Hrec p' q'); auto; injection Heq; intros H1 H2;
rewrite <- H1; rewrite <- H2; rewrite plus_comm;
auto) in
(intros w; elim w; clear w;
[ T_local
| T_local
| simpl in |- *; intros p q Heq; injection Heq; intros H1 H2;
rewrite <- H1; rewrite <- H2; auto with * ]).
Qed.

Theorem interp_non_zero :
forall w : Qpositive,
exists p : nat, (exists q : nat, Qpositive_i w = (S p, S q)).