TY  - JOUR
AU  - H. H. Pu
AU  - H. W. Pu
TI  - On level sets of approximate derivative and approximate symmetric derivative
JO  - Colloquium Mathematicum
PY  - 1987
SP  - 139
EP  - 142
VL  - 54
IS  - 1
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/articles/10.4064/cm-54-1-139-142/
DO  - 10.4064/cm-54-1-139-142
LA  - en
ID  - 10_4064_cm_54_1_139_142
ER  -