@article{MZ_1987__196_173905,
     author = {D. Gnuschke-Hauschild},
     title = {On the {Angular} {Derivative} of {Analytic} {Functions.}},
     journal = {Mathematische Zeitschrift},
     pages = {591--601},
     publisher = {mathdoc},
     volume = {196},
     year = {1987},
     zbl = {0616.30033},
     url = {http://geodesic.mathdoc.fr/item/MZ_1987__196_173905/}
}