@article{GDZPPN00207768X,
title = {Ungel\"oste Probleme.},
journal = {Elemente der Mathematik},
volume = {26},
year = {1971},
pages = {58-58},
url = {http://dml.mathdoc.fr/item/GDZPPN00207768X}
}
Hadwiger, H.; Schneider, R. Ungelöste Probleme.. Elemente der Mathematik, Tome 26 (1971) p. 58. http://gdmltest.u-ga.fr/item/GDZPPN00207768X/