proposition: Lemma ffunMnE f n x : (f *+ n) x = f x *+ n.
proof: Proof. by rewrite -[n]card_ord -!sumr_const sum_ffunE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)