@article{700716,
     title = {On descriptive classification of functions},
     booktitle = {General Topology and its Relations to Modern Analysis and Algebra},
     series = {GDML\_Books},
     publisher = {Academia Publishing House of the Czechoslovak Academy of Sciences},
     address = {Praha},
     year = {1972},
     pages = {235-242},
     mrnumber = {MR0355956},
     zbl = {0309.54015},
     url = {http://dml.mathdoc.fr/item/700716}
}

Katětov, M. On descriptive classification of functions, dans General Topology and its Relations to Modern Analysis and Algebra, GDML_Books,  (1972), pp. 235-242. http://gdmltest.u-ga.fr/item/700716/