proposition: Lemma BQprod_div: x <> \0q -> x *q (y /q x) = y.
proof: Proof. move => h. rewrite /BQdiv (BQprodC y) (BQprodA xq (QS_inv xq) yq). by rewrite BQprod_inv1 // BQprod_1l. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)