%0 Journal Article
%A H. H. Pu
%A H. W. Pu
%T On level sets of approximate derivative and approximate symmetric derivative
%J Colloquium Mathematicum
%D 1987
%P 139-142
%V 54
%N 1
%I mathdoc
%U http://geodesic.mathdoc.fr/articles/10.4064/cm-54-1-139-142/
%R 10.4064/cm-54-1-139-142
%G en
%F 10_4064_cm_54_1_139_142