unfold Qpositive_mult in |- *.
replace (Qpositive_i One) with (1, 1).
rewrite Heq.
repeat rewrite mult_1_l.
apply construct_correct; auto with *.
simpl in |- *; auto.
Qed.

Theorem Qpositive_mult_sym :
forall w w' : Qpositive, Qpositive_mult w w' = Qpositive_mult w' w.