@article{GDZPPN00221556X,
title = {Die windschiefen Fl\"achen konstanter Dralls in der Normalenkongruenz einer Fl\"ache.},
journal = {Manuscripta mathematica},
volume = {2},
year = {1970},
pages = {163-180},
zbl = {0182.54704},
url = {http://dml.mathdoc.fr/item/GDZPPN00221556X}
}
Giering, Oswald. Die windschiefen Flächen konstanter Dralls in der Normalenkongruenz einer Fläche.. Manuscripta mathematica, Tome 2 (1970) pp. 163-180. http://gdmltest.u-ga.fr/item/GDZPPN00221556X/