De Wulf, Maurice
Dover Publications, Inc., 1922
Buku Teks
Tidman, Paul
Wadsworth, 1999
Buku Teks
Hausman, Alan
Wadsworth and Cengage Learning, 2013
Buku Teks
Randall, John Herman
Barnes & Noble, 1957
Buku Teks
Brightman, Edgar Sheffield
Holt, Rinehart and Winston, 1961
Buku Teks