@article{article0ee6a952,
title   = {Minimal number of preimages under maps of surfaces},
author = {Bogatyi, Semeon A. and Gonçalves, Daciberg Lima and Kudryavtseva, Elena A.},
year = {2004},
doi = {10.1023/B:MATN.0000015017.47636.4b},
journal   = {Mathematical Notes}
}