@article{CM_1935__2__50_0,
     author = {Hopf, Heinz},
     title = {\"Uber die {Drehung} der {Tangenten} und {Sehnen} ebener {Kurven}},
     journal = {Compositio Mathematica},
     pages = {50--62},
     publisher = {Johnson Reprint Corporation},
     volume = {2},
     year = {1935},
     zbl = {0011.17702},
     language = {de},
     url = {http://www.numdam.org/item/CM_1935__2__50_0/}
}