Enciclopedia garzanti universale : vol. 1, A-N
Garzanti, 1962
Buku Referensi
The World book encyclopedia : volume 13, N-O
Field Enterprises Educational Corporation, 1963
Buku Referensi
The Encyclopedia Americana : volume 1
Americana Corporation, 1977
Buku Referensi
The Encyclopedia Americana : volume 1
Americana Corporation, 1964
Buku Referensi
Encyclopaedia Britannica : volume 1
Encyclopaedia Britannica Inc., 1967
Buku Referensi