proposition: Lemma sdprod_card G A B : A ><| B = G -> (#|A| * #|B|)%N = #|G|.
proof: Proof. by case/sdprodP=> [[H K -> ->] <- _ /TI_cardMg]. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)