On the points of non-differentiability of convex functions.
(English).Commentationes Mathematicae Universitatis Carolinae,
vol. 45
(2004),
issue 4,
pp. 727-734
[2] Zajíček L.: On the differentiability of convex functions in finite and infinite dimensional spaces. Czechoslovak Math. J. 29 (104) (1979), 340-348. MR 0536060