@article{MAN_1931__105_159521,
     author = {H. Graf and B. Sauer},
     title = {\"Uber {Fl\"achenverbiegung} in {Analogie} zur {Verknickung} offener {Facettenflache}},
     journal = {Mathematische Annalen},
     pages = {499--535},
     publisher = {mathdoc},
     volume = {105},
     year = {1931},
     zbl = {0002.41101},
     url = {http://geodesic.mathdoc.fr/item/MAN_1931__105_159521/}
}