@article{CMH_1959__33_139166,
     author = {Walter F\"assler},
     title = {\"Uber die {Normaltorsion} von {Fl\"achen} im vierdimensionalen euklidischen {Raum.}},
     journal = {Commentarii mathematici Helvetici},
     pages = {89--108},
     publisher = {mathdoc},
     volume = {33},
     year = {1959},
     zbl = {0084.17903},
     url = {http://geodesic.mathdoc.fr/item/CMH_1959__33_139166/}
}