proposition: Lemma big_ord0 P F : \big[op/idx]_(i < 0 | P i) F i = idx.
proof: Proof. by rewrite big_pred0 => [|[]]. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)