proposition: Lemma ex_pseries_plus (a b : nat -> V) (x : K) : ex_pseries a x -> ex_pseries b x -> ex_pseries (PS_plus a b) x.
proof: Proof. move => [la Ha] [lb Hb]. exists (plus la lb). by apply is_pseries_plus. Qed.
imports: Coq(Reals Psatz ssreflect) Rcomplements Rbar Lim_seq Lub Hierarchy Continuity Derive Seq_fct Series