Browning, Carl H., author
Oxford University Press, 1937
Buku Referensi
Metcalf, Richard W., author
Harcourt Brace Jovanovich, 1990
Buku Teks
Klein, Cornelis, author
John Wiley & Sons, 1985
Buku Referensi
Calder, Ritchie
The university Chichago Press, 1962
Buku Teks SO
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