Balwin, Robert
Cipta Manunggal, 2002
Buku Teks
Varwell, D. W. P.
MacDonald and Evans, 1978
Buku Teks
Weatheritt, Mollie
Croom Helm, 1986
Buku Teks
Chopra, Deepak
Harmony Books, 1995
Buku Teks
Stout, Hiram Miller
Oxford University Press, 1953
Buku Teks