@article{700658,
     title = {Some results on distance functions},
     booktitle = {General topology and its relations to modern analysis and algebra IV},
     series = {GDML\_Books},
     publisher = {Society of Czechoslovak Mathematicians and Physicist},
     address = {Praha},
     year = {1977},
     pages = {[371]-380},
     mrnumber = {MR0458373},
     zbl = {0367.54011},
     url = {http://dml.mathdoc.fr/item/700658}
}

Reichel, H. C. Some results on distance functions, dans General topology and its relations to modern analysis and algebra IV, GDML_Books,  (1977), pp. [371]-380. http://gdmltest.u-ga.fr/item/700658/