proposition: Lemma BQsum_0l x: ratp x -> \0q +q x = x.
proof: Proof. move => xq; move: (xq) => /BQ_P [px nx dx cx]. rewrite /BQsum /BQ_zero /BQ_of_Z pr1_pair pr2_pair BZprod_0l (BZprod_1l nx). by rewrite (BZprod_1l (BZps_sBZ dx)) (BZsum_0l nx) BQ_pr2. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)