Hubbard, L. Ron, 1911-1986
Bridge Publications, Inc., 2012
Buku Referensi
KITL Press, 2007
Buku Teks
Earl, G. W. (George Windsor), 1865-
Oxford University Press, 1971
Buku Teks
Freeman, J. D.
Thomas Avery ,
Buku Teks
Stead, David G.
Angus and Robertson, 1963
Buku Teks