International Labour Office, 1969
Buku Teks
Blossey, Ralf, author
Springer, 2012
eBooks
Donner, Jorn, 1933-, author
Dover Publications, 1972
Buku Teks
edited by Georg Hass, Maurice H. Francombe, John L. Vossen
Academic Press , 1982
Buku Teks
Magnenat-Thalmann, Nadia, 1946-, author
Springer-Verlag, 1990
Buku Teks