@article{MZ_1977__153_172474,
     author = {Burton Rodin and Stefan E. Warschawski},
     title = {Extremal {Length} and {Univalent} {Functions,} {I.} {The} {Angular} {Derivative.}},
     journal = {Mathematische Zeitschrift},
     pages = {1--18},
     year = {1977},
     volume = {153},
     zbl = {0384.30006},
     url = {http://geodesic.mathdoc.fr/item/MZ_1977__153_172474/}
}