@article{MM2_1977__21_154458,
     author = {Christoph L\"ubbert},
     title = {\"Uber geschlossene affine {Zwangl\"aufe} in der {Ebene.}},
     journal = {Manuscripta mathematica},
     pages = {101--116},
     publisher = {mathdoc},
     volume = {21},
     year = {1977},
     zbl = {0383.53002},
     url = {http://geodesic.mathdoc.fr/item/MM2_1977__21_154458/}
}