@Book{Lichtenstein1922,
author  = "Lichtenstein, Leon",
title   = "Mathematische Probleme in der Theorie der Figur der Himmelskörper",
year    = "1922",
address = "München",
series  = "Sitzungsberichte",
volume  = "1921,2",
url     = "https://publikationen.badw.de/de/003399217",
}