Substitutes and stability for matching with contracts

We consider the matching problem with contracts of Hatfield and Milgrom (2005), and we introduce new concepts of bilateral and unilateral substitutes. We show that bilateral substitutes is a sufficient condition for the existence of a stable allocation in this framework. However, the set of stable allocations does not form a lattice under this condition, and there does not necessarily exist a doctor-optimal stable allocation. Under a slightly stronger condition, unilateral substitutes, the set of stable allocations still does not necessarily form a lattice with respect to doctors’ preferences, but there does exist a doctor-optimal stable allocation, and other key results such as incentive compatibility and the rural hospitals theorem are recovered. Journal of Economic Literature Classification Numbers: C78, D44.