proposition: Lemma submod_mx_repr : mx_repr G (submod_mx Umod).
proof: Proof. rewrite /submod_mx; split=> [|x y Gx Gy /=]. by rewrite repr_mx1 mulmx1 val_submodK. rewrite -in_submodJ; first by rewrite repr_mxM ?mulmxA. by rewrite mxmodule_trans ?val_submodP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div choice fintype tuple finfun bigop prime) mathcomp(ssralg poly polydiv finset fingroup morphism) mathcomp(perm automorphism quotient finalg action zmodp) mathcomp(commutator cyclic center pgroup matrix mxalgebra) mathcomp(mxpoly)