proposition: Lemma sub_series_geq m n : (m <= n)%N -> series n - series m = \sum_(m <= k < n) u_ k.
proof: Proof. by move=> /subnK<-; rewrite series_addn addrAC subrr add0r. Qed.
imports: mathcomp(all_ssreflect ssralg ssrint ssrnum matrix) mathcomp(interval rat) mathcomp(mathcomp_extra boolp classical_sets functions) mathcomp(set_interval) reals ereal signed topology normedtype landau