proposition: Lemma realrM x y : y != 0 -> y \is real -> (x * y \is real) = (x \is real).
proof: Proof. by move=> y_neq0 yR; rewrite mulrC realMr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(ssrAC div fintype path bigop order finset fingroup) mathcomp(ssralg poly)