Lipsey, R. G., & Chrystal, K. A. (1999). Principles of economics (9th ed.). Oxford University Press.

Lipsey, Richard G., and K. Alec Chrystal. Principles of Economics. 9th ed. Oxford ; New York: Oxford University Press, 1999.

Lipsey, Richard G., and K. Alec Chrystal. Principles of Economics. 9th ed. Oxford University Press, 1999.