Hardwick, P., & Langmead, J. a. K. B. (1999). An introduction to modern economics (5th ed.). Prentice hall.

Hardwick, Philip, and John and Khan Bhadur Langmead. An Introduction to Modern Economics. 5th ed. Harlow, England: Prentice hall, 1999.

Hardwick, Philip, and John and Khan Bhadur Langmead. An Introduction to Modern Economics. 5th ed. Prentice hall, 1999.