proposition: Lemma algMixin (R : ringType) (A : algType R) (B : lalgType R) (f : B -> A) : phant B -> injective f -> {morph f : x y / x * y} -> scalable f -> forall k (x y : B), k *: (x * y) = x * (k *: y).
proof: Proof. by move=> _ inj_f fM fZ a x y; apply: inj_f; rewrite !(fM, fZ) scalerAr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)