@article{MZ_1980__170_172911,
     author = {Glenn Schober and Peter Duren},
     title = {Nonvanishing {Univalent} {Functions.}},
     journal = {Mathematische Zeitschrift},
     pages = {195--216},
     publisher = {mathdoc},
     volume = {170},
     year = {1980},
     zbl = {0411.30010},
     url = {http://geodesic.mathdoc.fr/item/MZ_1980__170_172911/}
}