proposition: Lemma big_ord_widen n1 n2 (F : nat -> R) : n1 <= n2 -> \big[op/idx]_(i < n1) F i = \big[op/idx]_(i < n2 | i < n1) F i.
proof: Proof. by move=> le_n12; apply: (big_ord_widen_cond (predT)). Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)