proposition: Lemma sub_double_series n : series n.*2 - series n = \sum_(n <= k < n.*2) u_ k.
proof: Proof. by rewrite sub_series_geq// -addnn leq_addl. 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