proposition: Lemma pprodWC A B G : pprod A B = G -> B * A = G.
proof: Proof. by case/pprodP=> _ <- /normC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)