proposition: Lemma prodr_const (I : finType) (A : pred I) x : \prod_(i in A) x = x ^+ #|A|.
proof: Proof. by rewrite big_const -iteropE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)