Artikel Jurnal
Smarandache, Florentin, author
Hexis, 2005
Buku Teks
Omnes, Roland, author
Princeton University Prees, 1994
Buku Teks
Townsend, John S., author
University Science Books, 2012
Buku Teks
Bongaarts, Peter, author
Springer International Publishing, 2015
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