Hardy, Frank
Gold Star Publication, 1971
Koleksi Publik
Hood, Jack B.
West Publishing, 1990
Buku Teks
Hardy, Randall W.
Westview Press, 1978
Buku Teks
McNeil, William Hardy
The Twentieth Century Fund, 1957
Buku Teks
Ivamy, E.R. Hardy, author
Butterworth, 1971
Buku Teks