proposition: Lemma mulR_eq0' (x y : R) : (x * y == 0) = ((x == 0) || (y == 0)).
proof: Proof. apply/idP/idP => [/eqP/mulR_eq0[]/eqP-> //|]; first by rewrite orbT. by case/orP => /eqP ->; rewrite ?mulR0 ?mul0R. Qed.
imports: mathcomp(all_ssreflect ssralg ssrnum) Reals mathcomp(lra) mathcomp(Rstruct)