Downward, Michael
Taylor and Francis, 1998
Buku Teks
Schagrin, Morton L.
Random House , 1968
Buku Teks
Ayer, Alfred Jules, 1910-1989
Dover, 1952
Buku Teks
Ayer, Alfred Jules, 1910-1989
Penguin Books, 1980
Buku Teks
Barwise, Jon, editor
CSLI Publications, 2000
Buku Teks