%0 Journal Article %A W. Wojtyński %T A property of differentiable functions %J Colloquium Mathematicum %D 1966 %P 303-306 %V 15 %N 2 %I mathdoc %U http://geodesic.mathdoc.fr/articles/10.4064/cm-15-2-303-306/ %R 10.4064/cm-15-2-303-306 %G en %F 10_4064_cm_15_2_303_306