Weadh, Robert C
Harvard University Press, 1966
Buku Teks
Miller, Robert W.
Prentice-Hall, 1997
Buku Teks
Donnelly, Thomas C.
The University of New mexico Press, 1953
Buku Teks
Pick, James B., author
Westview , 1989
Buku Referensi
Dullemen, Inez van, author
Querido, 1988
Buku Teks