proposition: Lemma big_geq_mkord (m n : nat) (P : pred nat) F : \big[op/idx]_(m <= i < n | P i) F i = \big[op/idx]_(i < n | P i && (m <= i)) F i.
proof: Proof. by rewrite (@big_nat_widenl _ 0)// big_mkord. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)