Abeyratne, Ruwantissa
Springer, 2012
eBooks
Speas, R. Dixon
MGraw-Hill , 1955
Buku Teks
Pigou, A.
MacMillan, 1947
Buku Teks
edited by Victor R. Fuchs
University of Chicago, 1982
Buku Teks
edited by A.J. Culyer and K.G. Wright
Martin Robertson, 1978
Buku Teks