Presidencia de la Republica , 1992
Buku Referensi
Tucker, William P.
University of Minnesota Press, 1958
Buku Teks
edited by James W. Wilkie, Michael C. Meyer and Edna Monzon de Wilkie
University of California Press, 1976
Buku Teks
Foster, George M., author
Little, Brown, 1967
Buku Teks
Griffiths, Brian, author
Praeger , 1972
Buku Teks