Newby, Michael
Cambridge University Press, 1988
Buku Teks SO
Simpson, David
Oxford University Press , 1986
Buku Teks SO
Kenyon, John Samuel
Merriam-Webster ; G. & C. Merriam Co., 1953
Buku Referensi
Lutz, William D.
Cambridge University Press, 1994
Buku Referensi
Wolfram, Walt, 1941-
Wiley Balckwell, 2016
Buku Teks SO