\begin{definition}[Definition:Oscillation/Real Space/Oscillation at Point/Epsilon]
Let $X$ and $Y$ be real sets.
Let $f: X \to Y$ be a real function.
Let $x \in X$.
The '''oscillation of $f$ at $x$''' is defined as:
:$\ds \map {\omega_f} x := \inf \set {\map {\omega_f} {\openint {x - \epsilon} {x + \epsilon} \cap X}: \epsilon \in \R_{>0} }$
where $\map {\omega_f} {\openint {x - \epsilon} {x + \epsilon} \cap X}$ denotes the oscillation of $f$ on $\openint {x - \epsilon} {x + \epsilon} \cap X$.
\end{definition}