proposition: Lemma prod_nat_const_nat n1 n2 n : \prod_(n1 <= i < n2) n = n ^ (n2 - n1).
proof: Proof. by rewrite big_const_nat -Monoid.iteropE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)