proposition: Lemma rcosetM A x y : A :* (x * y) = A :* x :* y.
proof: Proof. by rewrite -mulg_set1 mulgA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq choice) mathcomp(fintype div path tuple bigop prime finset)