Easton, David
Knopf, 1971
Buku Teks
edited by Paul Boreham, Geoffrey Stokes and Richard Hall
Pearson-Longman, 2004
Buku Teks
Clinton, Richard L.
Lexington Books, 1972
Buku Teks
Ebenstein, William
Rinehart, 1963
Buku Teks
Warburton, Nigel, 1962-
Routledge, 2000
Buku Teks