Hayes, Carlton J. H., author
Macmillan, 1932
Buku Teks
Ferris, Paul
Hutchinson , 1968
Buku Teks
John Wiley & Sons, 1982
Buku Teks
Pounds, Norman J. G., author
Frederick A. Praeger, 1964
Buku Teks
Coudenhove-Kalergi, Richard
Seewald Verlag, 1972
Buku Teks