Shuster, George N.
Harper & Row,Publishers, 1963
Buku Teks
Paris : Unesco Coupon
Majalah, Jurnal, Buletin
Sandage, C.H.
Richard D. Irwin, 1961
Buku Teks
Ahmed, Akbar S., author
Routledge, 1995
Buku Teks
Huntington, Samuel P., author
The Belknap Press, 1981
Buku Teks