@article{10_4064_cm_43_1_155_160,
     author = {H. H. Pu and H. W. Pu},
     title = {On the set where an approximate derivative is a derivative},
     journal = {Colloquium Mathematicum},
     pages = {155--160},
     publisher = {mathdoc},
     volume = {43},
     number = {1},
     year = {1980},
     doi = {10.4064/cm-43-1-155-160},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/cm-43-1-155-160/}
}