Section PS_minus.
Context {K : AbsRing} {V : NormedModule K}.
Definition PS_minus (a b : nat -> V) (n : nat) : V := plus (a n) (opp (b n)).
End PS_minus.

Lemma PSeries_minus (a b : nat -> R) (x : R) :
ex_pseries a x -> ex_pseries b x
-> PSeries (PS_minus a b) x = PSeries a x - PSeries b x.