proposition: Lemma BQsum_CA x y z: ratp x -> ratp y -> ratp z -> x +q (y +q z) = y +q (x +q z).
proof: Proof. by move => xz yz zz;rewrite (BQsumA xz yz zz) (BQsumA yz xz zz) (BQsumC x y). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)