\begin{definition}[Definition:Positive Series]
Let $\ds s = \sum_{n \mathop = 1}^\infty a_n$ be a series in the real numbers $\R$.
The series $s$ is a '''positive series''' {{iff}} 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 (strictly) positive or (strictly) negative.
\end{definition}