1. Gorman, W. M.: Preference, revealed preference and indifference. In: Chipman, Hurwicz, Richter, Sonnenschein (eds.) Preferences, utility and demand. New York: Harcourt 1971
2. Sonneschein, H. F.: On the continuity of demand functions which satisfy the strong axiom of revealed preference. In: Chipman, Hurwicz, Richter and Sonnenschein (eds.) Preferences, utility and demand. New York: Harcourt 1971