proposition: Lemma big_nat m n F : \big[op/idx]_(m <= i < n) F i = \big[op/idx]_(m <= i < n | m <= i < n) F i.
proof: Proof. by rewrite big_nat_cond big_andbC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)