proposition: Lemma BQdiff_div a b c: ratp a -> ratp b -> ratp c -> c <> \0q -> a -q (b /q c) = (a *q c -q b) /q c.
proof: Proof. move => aq bq cq cnz; move:(QSo bq) => obq. by rewrite /BQdiff (BQopp_div_l bq cq); apply: BQsum_div. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)