Cambridge University Press, 2019
eBooks
Okun, Arthur M., author
C.C. Norton, 1969
Buku Teks
Cambridge University Press, 2019
eBooks
edited by E.K. Fisk and H. Osman-Rani
Oxford University Press, 1982
Buku Teks
Gough, Ian, author
Macmillan, 1992
Buku Teks