The Encyclopedia of philosophy: volumes 5 and 6
editor in chief Paul Edward
MacMilan, 1972
 Buku Referensi
The Encyclopedia Americana : the international reference work, volume 6
Americana Corporation, 1960
 Buku Referensi
International military and defense encyclopedia; Volume 6
editor-in-chief, Trevor N. Dupuy
Brassey's, 1993
 Buku Referensi
The Encyclopedia Americana : the international reference work, volume 5
Americana Corporation, 1960
 Buku Referensi
International military and defense encyclopedia; Volume 5
editor-in-chief, Trevor N. Dupuy
Brassey's, 1993
 Buku Referensi