proposition: Lemma ker_dprodm : 'ker dprodm = [set a * b^-1 | a in H, b in K & fH a == fK b].
proof: Proof. exact: ker_cprodm. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)