proposition: Lemma BQdiv_sign x y: ratp x -> ratp y -> BQsign (x /q y) = (BQsign x) *z (BQsign y).
proof: Proof. by move => xq yq; rewrite /BQdiv (BQprod_sign xq (QS_inv yq)) (BQinv_sign yq). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)