proposition: Lemma big_nseq I n a (F : I -> R): \big[op/idx]_(i <- nseq n a) F i = iter n (op (F a)) idx.
proof: Proof. exact: big_nseq_cond. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat seq path) mathcomp(div fintype tuple finfun)