(** * Operations *)
(** Additive operators *)
Section Properties2.
Context {K : AbsRing} {V : NormedModule K}.

Lemma is_series_minus (a b : nat -> V) (la lb : V) :
is_series a la -> is_series b lb
-> is_series (fun n => plus (a n) (opp (b n))) (plus la (opp lb)).