proposition: Lemma mcoeffMr g1 g2 k : (g1 * g2)@_k = \sum_(k2 <- msupp g2) \sum_(k1 <- msupp g1) (g1@_k1 * g2@_k2) *+ (k1 * k2 == k)%M.
proof: Proof. exact: mcoeffMrw. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path choice finset fintype finfun) mathcomp(tuple bigop ssralg ssrint ssrnum) xfinmap