proposition: Lemma morphpre_mx_repr : mx_repr (f @*^-1 G) (rG \o f).
proof: Proof. split=> [|x y]; first by rewrite /= morph1 repr_mx1. case/morphpreP=> Dx Gfx; case/morphpreP=> Dy Gfy. by rewrite /= morphM ?repr_mxM. 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)