@article{JDM_1940__50_146248,
     author = {M. Pinl},
     title = {Zur {Theorie} der halbisotropen {Fl\"achen} in {R4.}},
     journal = {Jahresbericht der Deutschen Mathematiker-Vereinigung},
     pages = {65--78},
     publisher = {mathdoc},
     volume = {50},
     year = {1940},
     zbl = {66.0837.01},
     url = {http://geodesic.mathdoc.fr/item/JDM_1940__50_146248/}
}