proposition: Lemma sumrMnr x I r P (F : I -> nat) : \sum_(i <- r | P i) x *+ F i = x *+ (\sum_(i <- r | P i) F i).
proof: Proof. by rewrite (big_morph _ (mulrnDr x) (erefl _)). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)