proposition: Lemma morphim_dprodmr B : B \subset K -> dprodm @* B = fK @* B.
proof: Proof. exact: morphim_cprodmr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)