proposition: Lemma sum_nat_mulnr [I : finType] (A : pred I) (n : nat) (F : I -> nat) : (n * \sum_(i in A) F i)%N = \sum_(i in A) n * F i.
proof: Proof. by elim/big_ind2 : _ => // [|? m1 ? m2 <- <-]; rewrite ?muln0 ?mulnDr. Qed.
imports: Coq(Setoid Morphisms) mathcomp(all_ssreflect) GraphTheory(edone)