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Page one publishing pte ltd, 2011
Buku Referensi
h.f.ullman, 2010
Buku Referensi
Crosbie, Michael J., author
Rockport Publishers, 1998
Buku Teks
Tobias Waltjen, Walter Pokorny, Thomas Zelger, Karl Tonghele
Springer, 2007
Buku Referensi
State University of New York Press , 1988
Buku Teks