Definition:Positive Series

Definition
Let $\displaystyle s = \sum_{n \mathop = 1}^\infty a_n$ be a series in the real numbers $\R$.

The series $s$ is a positive series either:
 * $\forall n \in \N: a_n > 0$

or:
 * $\forall n \in \N: a_n < 0$

That is, if all terms of $\sequence {a_n}$ are either all positive or negative.