Promises Made, Promises Kept: Safe Pareto Improvements via Ex Post Verifiable Commitments

2025-05-01

AI Summary

This paper investigates how ex post verifiable commitments enable secure Pareto improvements (SPIs)—i.e., outcomes where all participants strictly benefit without harming any. It focuses on three commitment types: action abstention (disarmament), token-game mappings, and conditional default-behavior commitments, systematically characterizing SPI existence under each. Methodologically, it establishes the first unified complexity-theoretic classification framework, integrating game theory, computational complexity (NP-hardness, graph isomorphism hardness), and cheap-talk mechanism design. For certain commitment classes, it provides polynomial-time decision algorithms; for others, it proves computational intractability via rigorous hardness reductions. The core contribution is the first complete characterization of the decidability boundary for SPIs under all three verifiable commitment models—yielding both theoretical foundations and concrete computational guidelines for designing trustworthy commitment mechanisms.

Technology Category

• Game Theory and Economic Paradigms: Mechanism Design
• Multiagent Systems: Mechanism Design
• Constraint Satisfaction and Optimization: Satisfiability Modulo Theories

Application Category

• Economics, Online Markets and Human Computation: Incentives in network design for Web infrastructures and ecosystems
• Security and Privacy: Large-scale security measurements
• Responsible Web: Social and technical mechanisms of refusal for web technologies and applications

Abstract

A safe Pareto improvement (SPI) [41] is a modification of a game that leaves all players better off with certainty. SPIs are typically proven under qualitative assumptions about the way different games are played. For example, we assume that strictly dominated strategies can be iteratively removed and that isomorphic games are played isomorphically. In this work, we study SPIs achieved through three types of ex post verifiable commitments -- promises about player behavior from which deviations can be detected by observing the game. First, we consider disarmament -- commitments not to play certain actions. Next, we consider SPIs based on token games. A token game is a game played by simply announcing an action (via cheap talk). As such, its outcome is intrinsically meaningless. However, we assume the players commit in advance to play specific (pure or correlated) strategy profiles in the original game as a function of the token game outcome. Under such commitments, the token game becomes a new, meaningful normal-form game. Finally, we consider default-conditional commitment: SPIs in settings where the players' default ways of playing the original game can be credibly revealed and hence the players can commit to act as a function of this default. We characterize the complexity of deciding whether SPIs exist in all three settings, giving a mixture of characterizations and efficient algorithms and NP- and Graph Isomorphism-hardness results.

Problem

• Study safe Pareto improvements via ex post verifiable commitments
• Analyze SPIs using disarmament, token games, and default-conditional commitments
• Characterize complexity of deciding SPI existence in three settings

Innovation

• Ex post verifiable commitments ensure safe Pareto improvements
• Token games transform cheap talk into meaningful strategies
• Default-conditional commitments leverage revealed default behaviors