edited by James Flood, Julie M. Jensen, Diane Lapp, James R. Squire
Macmillan, 1991
Buku Referensi
edited by Merlin C. Wittrock; a project of the American Educational Research Association
Macmillan Library Reference USA, 1986
Buku Referensi
edited by Douglas A. Grouws
Macmillan Library Reference, 1992
Buku Referensi
Littlewood, William
Cambridge Uniiversity Press , 1983
Buku Teks
Littlewood, William
Cambridge University Press, 1994
Buku Teks