A Complexity Approach for Core-Selecting Exchange under Conditionally Lexicographic Preferences

International audienceCore-selection is a crucial property of rules in the literature of resource allocation. It is also desirable, from the perspective of mechanism design, to address the incentive of agents to cheat by misreporting their preferences. This paper investigates the exchange problem where (i) each agent is initially endowed with (possibly multiple) indivisible goods, (ii) agents' preferences are assumed to be conditionally lexicographic, and (iii) side payments are prohibited. We propose an exchange rule called augmented top-trading-cycles (ATTC), based on the original TTC procedure. We first show that ATTC is core-selecting and runs in polynomial time with respect to the number of goods. We then show that finding a beneficial misreport under ATTC is NP-hard. We finally clarify relationship of misreporting with splitting and hiding, two different types of manipulations, under ATTC

Aggregating Conditionally Lexicographic Preferences on Multi-issue Domains

International audienceOne approach to voting on several interrelated issues consists in using a language for compact preference representation, from which the voters’ preferences are elicited and aggregated. A language usually comes with a domain restriction. We consider a well-known restriction, namely, conditionally lexicographic preferences, where both the relative importance between issues and the preference between values of an issue may depend on the values taken by more important issues. The naturally associated language consists in describing conditional importance and conditional preference by trees together with conditional preference tables. In this paper, we study the aggregation of conditionally lexicographic preferences, for several voting rules and several restrictions of the framework. We characterize computational complexity for some popular cases, and show that in many of them, computing the winner reduces in a very natural way to a maxsat problem