Willoughby, Westel W.
John Hopkins Press, 1927
Buku Teks
Chesterman, Andrew
Cambridge University Press, 1991
Buku Teks
Tarlekar, G. H.
Motial Banarsidass Publishers, 1991
Buku Teks
Nowak, Norman D.
Praeger, 1970
Buku Teks
Jahoda, Marie
Dryden Press, 1955
Buku Teks