APA-referens (7:e uppl.)
Friedrich, P. (1970). Proto-indo-european trees: The arboreal system of a prehistoric people. University of Chicago Press.
Chicago-referens (17:e uppl.)
Friedrich, Paul. Proto-indo-european Trees: The Arboreal System of a Prehistoric People. Chicago: University of Chicago Press, 1970.
MLA-referens (9:e uppl.)
Friedrich, Paul. Proto-indo-european Trees: The Arboreal System of a Prehistoric People. University of Chicago Press, 1970.
Varning: dessa hänvisningar är inte alltid fullständigt riktiga.