proposition: Lemma RSp x y: realp x -> realp y -> realp (x *r y).
proof: Proof. move => pa pb. case/BR_i0P:pa => sa;case/BR_i0P:pb => sb. + exact:(BRps_sBR(RmsuS_prod sa sb)). + rewrite BRprodC; exact (BRm_sBR(RpmS_prod sb (BRms_sBRm sa))). + exact (BRm_sBR((RpmS_prod sa (BRms_sBRm sb)))). + exact:(BRp_sBR(RpS_prod sa sb)). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat)