proposition: Lemma dprodmEr b : b \in K -> dprodm b = fK b.
proof: Proof. exact: pprodmEr. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq div) mathcomp(choice fintype bigop finset fingroup morphism) mathcomp(quotient action)