proposition: Lemma expr_sum x (I : Type) (s : seq I) (P : pred I) F : x ^+ (\sum_(i <- s | P i) F i) = \prod_(i <- s | P i) x ^+ F i :> R.
proof: Proof. exact: (big_morph _ (exprD _)). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)