Halverson, william H
Random House, 1969
Buku Teks
Randall, John Herman, author
Barnes & Noble, 1957
Buku Teks
Brightman, Edgar Sheffield
Holt, Rinehart and Winston, 1961
Buku Teks
Patrick, George Thomas White, author
George Allen and Unwin, 1925
Buku Teks
Routledge, 2000
Buku Referensi