Benson, George C.S., author
Harvard University Press, 1935
Buku Teks
Goodnow, Henry Frank
Yale University Press 1, 1964
Buku Teks
R. A. W. Rhodes [and others]
Open University press, 2003
Buku Teks
State University of New York Press, 2006
Buku Teks
Amerasinghe, Chittharanjan Felix, 1933-, author
Clarendon Press, 1988
Buku Teks