Cheit, Earl F.
John Wiley , 1961
Buku Teks
D.C. Heath and Company, 1976
Buku Teks
Rolph, Earl R.
N.Y. The Ronald Press , 1961
Buku Teks
John Wiley & Sons, 1981
Buku Teks
edited by Earl Leslie Griggs and Clifford H. Prator
University of California Press, 1952
Buku Teks