proposition: Lemma rregMr (a b: R) : rreg (a * b) -> rreg a.
proof: Proof. by move=> rab c c' eq_ca; apply/rab; rewrite !mulrA eq_ca. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq path) mathcomp(ssralg fintype finfun perm matrix bigop zmodp mxalgebra) mathcomp(choice poly polydiv mxpoly binomial)