@article{10_21136_CMJ_1971_101037,
     author = {Preiss, David},
     title = {Approximate derivatives and {Baire} classes},
     journal = {Czechoslovak Mathematical Journal},
     pages = {373--382},
     publisher = {mathdoc},
     volume = {21},
     number = {3},
     year = {1971},
     doi = {10.21136/CMJ.1971.101037},
     mrnumber = {0286951},
     zbl = {0221.26007},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1971.101037/}
}