Soltau, Roger H.
Longmans, Green , 1951
Buku Teks
Soltau, Roger H.
Longmans, Green , 1960
Buku Teks
Dyke, Vernon van, author
Nelson, 1992
Buku Teks
Laski, Harold J., author
George Allen and Unwin, 1960
Buku Teks
Wilson, Graham K., author
Chatham House, 1985
Buku Teks