November 13 (10:00-11:00) room C.510 (new building, 5th floor)
Tom Demeulemeester (University of Lausanne, Switzerland)
Pairwise efficiency and monotonicity imply Pareto efficiency in (probabilistic) object allocation
We consider object allocation problems with capacities (see, e.g., Abdulkadiroglu and Sönmez, 1998; Basteck, 2025) where objects have to be assigned to agents. We show that if a lottery rule satisfies ex-post non-wastefulness and probabilistic (Maskin) monotonicity, then ex-post pairwise efficiency is equivalent to ex-post Pareto efficiency. This result allows for a strengthening of various existing characterization results, both for lottery rules and deterministic rules, by replacing (ex-post) Pareto efficiency with (ex-post) pairwise efficiency, e.g., for characterizations of the Random Serial Dictatorship rule (Basteck, 2025), Trading Cycles rules (Pycia and Ünver, 2017), and Hierarchical Exchange rules (Pápai, 2000).
The talk is based on joint work with Bettina Klaus, and on the paper https://arxiv.org/pdf/2508.05340 .