Choice functions and hard choices
研究了当决策者无法从备选方案中做出合理选择时的艰难选择情境，通过分析可能无法选出非空集合的选择函数，对两种经典选择规则进行了新的刻画，有助于理解艰难选择产生的条件。
A hard choice is a situation in which an agent is unable to make a justifiable choice from a given menu of alternatives. Our objective is to present a systematic treatment of the axiomatic structure of such situations. To do so, we draw on and contribute to the study of choice functions that can be indecisive, i.e., that may fail to select a non-empty set for some menus. In this more general framework, we present new characterizations of two well-known choice rules, the maximally dominant choice rule and the top-cycle choice rule. Together with existing results, this yields an understanding of the circumstances in which hard choices arise.