@Book{Külpe1915,
author  = "Külpe, Oswald",
title   = "Zur Kategorienlehre. Vorgetragen am 6. Februar 1915",
year    = "1915",
address = "München",
series  = "Sitzungsberichte",
volume  = "1915,5",
url     = "https://publikationen.badw.de/de/003204492",
}