An extension of a theorem of Banach
The main result of the paper says that for nearly all functions which are continuous on the \(n\)-dimensional cube at each point \(P\) of the interior of the cube and for each direction upper and lower directional derivatives are \(+\infty\) and \(-\infty\), respectively. Here ``nearly all'' means except a sigma porous set.
scientific article; zbMATH DE number 938597