proposition: Lemma big_geq m n (P : pred nat) F : m >= n -> \big[op/idx]_(m <= i < n | P i) F i = idx.
proof: Proof. by move=> ge_m_n; rewrite /index_iota (eqnP ge_m_n) big_nil. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)