Bussmann, Hadumod
Routledge, 1996
Buku Referensi
McArthur, Thomas Burns
Cambridge University Press, 1983
Buku Teks SO
edited by Valerie Kinsella
Cambridge Uniiversity Press , 1979
Buku Teks
Croft, William
Cambridge University Press, 2004
Buku Teks
John E. Joseph
Edinburgh University Press, 2009
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