@article{ELMA_1990__45_6_141492,
     author = {H. Herold},
     title = {Charakterisierung der {Differentiale} mit geradlinigen {Isoklinen.}},
     journal = {Elemente der Mathematik},
     pages = {145--149},
     publisher = {mathdoc},
     volume = {45},
     number = {6},
     year = {1990},
     zbl = {0717.34003},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1990__45_6_141492/}
}