proposition: Lemma big_mkord n (P : pred nat) F : \big[op/idx]_(0 <= i < n | P i) F i = \big[op/idx]_(i < n | P i) F i.
proof: Proof. rewrite /index_iota subn0 -(big_map (@nat_of_ord n)). by congr bigop; rewrite /index_enum 2!unlock val_ord_enum. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)