@article{MZ_1965__90_170473,
     author = {Peter Lappan},
     title = {Some results on harmonic normal functions.},
     journal = {Mathematische Zeitschrift},
     pages = {155--159},
     publisher = {mathdoc},
     volume = {90},
     year = {1965},
     zbl = {0163.14002},
     url = {http://geodesic.mathdoc.fr/item/MZ_1965__90_170473/}
}