Gray, Harry B.
"Berlin: Walter de Gruyter, 1973",
Buku Teks
Tokheim, Roger L., author
Jakarta Erlangga 1995,
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Hein, Morris
"Monterey: Brooks Cole, 1984",
Buku Teks
Hill, John William, 1933-, author
Upper Saddle RIver Prentice Hall 1997,
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Theraja, B.L.
S. Chand & Company, 1996
Buku Teks