Coyne, John, author
Macmillan, 1987
Buku Teks
Napitupulu, Daniel, author
2004
Artikel Jurnal
Goldmann, Nahum, author
McGraw-Hill, 1992
Buku Teks
Downes, Colm, author
Cambridge university press, 2009
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Conroy, Pat, author
Doubleday, 2002
Buku Teks