@article{ELMA_1977__32_141200,
     author = {D. Kramer and Gerd Wegner},
     title = {Ein ebenes {Extremalproblem.}},
     journal = {Elemente der Mathematik},
     pages = {109--112},
     publisher = {mathdoc},
     volume = {32},
     year = {1977},
     zbl = {0353.52003},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1977__32_141200/}
}