Definition series_cv_abs {R : ConstructiveReals} (u : nat -> CRcarrier R)
: CR_cauchy R (CRsum (fun n => CRabs R (u n)))
-> { l : CRcarrier R & series_cv u l }.

Lemma series_cv_triangle : forall {R : ConstructiveReals}
(u : nat -> CRcarrier R) (s sAbs : CRcarrier R),
series_cv u s
-> series_cv (fun n => CRabs R (u n)) sAbs
-> CRabs R s <= sAbs.