\begin{definition}[Definition:Condensed Series]
Let $\sequence {a_n}: n \mapsto \map a n$ be a decreasing sequence of strictly positive terms in $\R$ which converges with a limit of zero.
That is, for every $n$ in the domain of $\sequence {a_n}$: $a_n > 0, a_{n + 1} \le a_n$, and $a_n \to 0$ as $n \to +\infty$.
The series:
:$\ds \sum_{n \mathop = 1}^\infty 2^n \map a {2^n}$
is called the '''condensed''' form of the series:
:$\ds \sum_{n \mathop = 1}^\infty a_n$
\end{definition}