\begin{definition}[Definition:Derivative/Higher Derivatives/Second Derivative/Notation]
The '''second derivative''' is variously denoted as:
:$\map {f''} \xi$
:$D^2 \map f \xi$
:$D_{xx} \map f \xi$
:$\map {\dfrac {\d^2} {\d x^2} } \xi$
If $y = \map f x$, then it can also expressed as $y''$:
:$y'' := \map {\dfrac \d {\d x} } {\dfrac {\d y} {\d x} }$
and written:
:$\dfrac {\d^2 y} {\d x^2}$
\end{definition}