Michael Saward, editor
Routledge, 2000
Buku Teks
Mayo, Henry B., author
Oxford University Press , 1960
Buku Teks
Sage Publications, 2012
eBooks
Dahl, Robert A., 1915-2014, author
The University of Chicago Press, 1956
Buku Teks
Cahn, Edmond
Vakils, Feffer and Simons, 1961
Buku Teks