Pick, James B., author
Westview , 1989
Buku Referensi
Rand McNally, [date of publication not identified]
Buku Referensi
Donnelly, Thomas C.
The University of New mexico Press, 1953
Buku Teks
Dullemen, Inez van, author
Querido, 1988
Buku Teks
Vaillant, George C., author
Penguin Books, 1944
Buku Teks