proposition: Lemma sumr_const_nat m n x : \sum_(n <= i < m) x = x *+ (m - n).
proof: Proof. by rewrite big_const_nat iter_addr_0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)