@Book{GrafSauer1924,
author  = "Graf, Heinrich and Sauer, Robert",
title   = "Dreifache Geradensysteme in der Ebene, welche Dreiecksnetze bilden",
year    = "1924",
address = "München",
series  = "Sitzungsberichte",
volume  = "1924,[13]",
url     = "https://publikationen.badw.de/en/003390827",
}