@Book{Löbell1944,
author  = "Löbell, Frank",
title   = "Differentialinvarianten bei Flächenabbildungen",
year    = "1944",
address = "München",
series  = "Sitzungsberichte",
volume  = "1943,11",
url     = "https://publikationen.badw.de/de/003395613",
}