proposition: Lemma fgmull g1 g2 : fgmul g1 g2 = \sum_(k1 <- msupp g1) \sum_(k2 <- msupp g2) g1 *M_[k1, k2] g2.
proof: Proof. by []. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path choice finset fintype finfun) mathcomp(tuple bigop ssralg ssrint ssrnum) xfinmap