User:Riedel~enwiki

Clarke derivative
$$ \partial_{Cl}\; \left. f\right|_{x_0}\left( h \right)\; =\; \stackrel{\displaystyle \lim \sup}{\scriptscriptstyle \stackrel{t \downarrow 0}{ x \to x_0} } \frac{\; f\left( x+th \right)-f\left( x \right)}{t} $$