Tham khảo There ain't no such thing as a free lunch

  1. 1 2 Safire, William On Language; Words Left Out in the Cold" New York Times, 2-14-1993
  2. ↑ Keyes, Ralph (2006). The Quote Verifier. New York: St. Martin's Press. tr. 70. ISBN 978-0-312-34004-9. 
  3. ↑ Smith, Chrysti M. (2006). Verbivore's Feast: Second Course. Helena, MT: Farcountry Press. tr. 131. ISBN 978-1-56037-404-6. 
  4. ↑ Friedman, Milton, There's No Such Thing as a Free Lunch, Open Court Publishing Company, 1975. ISBN 087548297X.
  5. ↑ Gwartney, James D.; Richard Stroup; Dwight R. Lee (2005). Common Sense Economics. New York: St. Martin's Press. tr. 8–9. ISBN 0-312-33818-X. 
  6. ↑ McConnell, Campbell R.; Stanley L. Brue (2005). Economics: principles, problems, and policies. Boston: McGraw-Hill Irwin. tr. 3. ISBN 978-0-07-281935-9. OCLC 314959936. Truy cập ngày 10 tháng 12 năm 2009.