\begin{definition}[Definition:Exponential Function/Real/Power Series Expansion]
Let $\exp: \R \to \R_{>0}$ denote the '''(real) exponential function'''.
The '''exponential function''' can be defined as a power series:
:$\exp x := \ds \sum_{n \mathop = 0}^\infty \frac {x^n} {n!}$
The number $\exp x$ is called the '''exponential of $x$'''.
\end{definition}