proposition: Lemma mcoeffUU k x : << x *g k >>@_k = x.
proof: Proof. by rewrite mcoeffU eqxx. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path choice finset fintype finfun) mathcomp(tuple bigop ssralg ssrint ssrnum) xfinmap