Isler, Hansruedi
Hafner Publishing Company, 1968
Buku Teks
Sage Publications, 1973
Majalah, Jurnal, Buletin
Auser, Cortland P.
Twayne, 1969
Buku Teks
Bueche, Frederick J., author
McGraw-Hill, 1980
Buku Teks
Sontheimer, Kurt
Fishcher Bucherei 1965
Buku Teks