proposition: Lemma QpmS_prod a b: inc a BQp -> inc b BQm -> inc (a *q b) BQm.
proof: Proof. move => aqp bqm. have h := (BQopp_negative2 bqm). rewrite -(BQopp_K (BQm_sBQ bqm)). rewrite - (BQopp_prod_r (BQp_sBQ aqp) (BQp_sBQ h)). apply: BQopp_positive2; apply:(QpS_prod aqp h). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)