1. See for example Paul A. Samuelson, “Constancy of the Marginal Utility of Income,”Studies in Mathematical Economics and Econometrics, in Memory of Henry Schultz (1942) edited by Oscar Lange, Francis McIntyre and Theodore O. Yntema, pp. 75–91, and reprinted inThe Collected Scientific Papers of Paul A. Samuelson, ed. Joseph E. Stiglitz, vol. 1 pp. 37–53.
2. Cf.Social Choice and Individual Values (1st ed. 1951 2nd ed. 1963) pp. 26–28.