RYAN, W. J. L.; SAMUELSON, Paul A. Economics: An Introductory Analysis.. Economica. 1952-05, roč. 19, čís. 74, s. 208. Dostupné online [cit. 2019-10-13]. ISSN0013-0427. doi:10.2307/2551073.
LEVITAN, Sar A.; TARSHIS, Lorie. The Elements of Economics: An Introduction to the Theory of Price and Employment.. Political Science Quarterly. 1948-06, roč. 63, čís. 2, s. 301. Dostupné online [cit. 2019-10-13]. ISSN0032-3195. doi:10.2307/2144851.
RYAN, W. J. L.; SAMUELSON, Paul A. Economics: An Introductory Analysis.. Economica. 1952-05, roč. 19, čís. 74, s. 208. Dostupné online [cit. 2019-10-13]. ISSN0013-0427. doi:10.2307/2551073.
LEVITAN, Sar A.; TARSHIS, Lorie. The Elements of Economics: An Introduction to the Theory of Price and Employment.. Political Science Quarterly. 1948-06, roč. 63, čís. 2, s. 301. Dostupné online [cit. 2019-10-13]. ISSN0032-3195. doi:10.2307/2144851.
RYAN, W. J. L.; SAMUELSON, Paul A. Economics: An Introductory Analysis.. Economica. 1952-05, roč. 19, čís. 74, s. 208. Dostupné online [cit. 2019-10-13]. ISSN0013-0427. doi:10.2307/2551073.
LEVITAN, Sar A.; TARSHIS, Lorie. The Elements of Economics: An Introduction to the Theory of Price and Employment.. Political Science Quarterly. 1948-06, roč. 63, čís. 2, s. 301. Dostupné online [cit. 2019-10-13]. ISSN0032-3195. doi:10.2307/2144851.