The objective of the paper is to analyze the formation of groups where individuals are allowed to engage in several groups at the same time. Each group is supposed to have specific rules or constitutions governing which members may join or leave it. Given these constitutions, we consider a group structure to be stable if no group is modified any more. We provide requirements on constitutions and players' preferences under which stable group structures are induced for sure. Furthermore, by embedding many-to-many matchings into our setting, we apply our model to job markets with labor unions. We find a variation of Roth's "polarization of interests" (cf. Roth, 1984) between employers and employees.
Mauleon, A., & et al. (2016). Constitutions and Social Networks. 2nd Mechanisms, Organizations, Markets and Agents (MOMA) Meeting, Universidad Pablo de Olavide, Sevilla (Spain). https://hdl.handle.net/2078.5/183685