proposition: Lemma BQprodBl x y z: ratp x -> ratp y -> ratp z -> (y -q z) *q x = (y *q x) -q (z *q x).
proof: Proof. by move => xq yq qgt0x; rewrite BQprodC (BQprodC y) (BQprodC z) BQprodBr. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)