Lopez, Violeta B.
University of the Philippines Press, 1976
Buku Teks
Postma, Antoon
Arnoldus Press, 1972
Buku Teks
Dozier, Edward P.
Holt, Rinehart and Winston, 1967
Buku Teks
Lopez-de-Silanes, Florencio
United Nations , 2002
Buku Teks
Princeton University Press , 1999
Buku Teks