proposition: Lemma mcoeffD k : {morph mcoeff k: x y / x + y}.
proof: Proof. exact: raddfD. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path choice finset fintype finfun) mathcomp(tuple bigop ssralg ssrint ssrnum) xfinmap