@article{ELMA_1969__24_140938,
     author = {E. Heil and W. Krautwald},
     title = {Konjugierte {Durchmesser} und extremale {Vierecke} konvexer {Bereiche.}},
     journal = {Elemente der Mathematik},
     pages = {97--103},
     publisher = {mathdoc},
     volume = {24},
     year = {1969},
     zbl = {0177.24801},
     url = {http://geodesic.mathdoc.fr/item/ELMA_1969__24_140938/}
}