@article{700865,
     title = {Borel subsets of metric separable spaces},
     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 = {1967},
     pages = {83-86},
     mrnumber = {MR0231723},
     zbl = {0204.00802},
     url = {http://dml.mathdoc.fr/item/700865}
}

Bukovský, L. Borel subsets of metric separable spaces, dans General Topology and its Relations to Modern Analysis and Algebra, GDML_Books,  (1967), pp. 83-86. http://gdmltest.u-ga.fr/item/700865/