(Group) Strategy-proofness and stability in many-to many marching markets

We study strategy-profness in many-to many matching markets. We prove that when firms have acyclical preferences over workers and both firms and workers have responsive preferences, the worker-optimal stable mechanism is group strategy-proof and Pareto optimal. Absent any assumption on workers’ references, an Adjusted Serial Dictatorship among workers is stable, group strategy-proof and Pareto optimal for workers. In both cases, the set of stable matchings is a singleton. We show that acyclicity is the minimal condition guaranteeing the existence of stable and strategy-proof mechanisms in many-to-many matching markets.