@article{MZ_1986__192_173757,
     author = {Wolfram Koepf},
     title = {On {Nonvanishing} {Univalent} {Functions} with {Real} {Coefficients.}},
     journal = {Mathematische Zeitschrift},
     pages = {575--580},
     year = {1986},
     volume = {192},
     zbl = {0599.30030},
     url = {http://geodesic.mathdoc.fr/item/MZ_1986__192_173757/}
}