proposition: Lemma comp_kHom_img K E f g : kHom K (g @: E) f -> kHom K E g -> kHom K E (f \o g).
proof: Proof. move=> /kHomP[fM idKf] /kHomP[gM idKg]; apply/kHomP; split=> [x y Ex Ey | x Kx]. by rewrite !lfunE /= gM // fM ?memv_img. by rewrite lfunE /= idKg ?idKf. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype tuple finfun bigop ssralg poly) mathcomp(polydiv finset fingroup morphism quotient perm) mathcomp(action zmodp cyclic matrix mxalgebra vector) mathcomp(falgebra fieldext separable)