@article{MZ_1974__137_172053,
     author = {Dennis A. Hejhal},
     title = {Universal {Covering} {Maps} for {Variable} {Regions.}},
     journal = {Mathematische Zeitschrift},
     pages = {7--20},
     publisher = {mathdoc},
     volume = {137},
     year = {1974},
     zbl = {0316.30009},
     url = {http://geodesic.mathdoc.fr/item/MZ_1974__137_172053/}
}