proposition: Lemma cprodJ A B x : (A \* B) :^ x = A :^ x \* B :^ x.
proof: Proof. by rewrite /cprod centJ conjSg -pprodJ; case: ifP => _ //; apply: imset0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)