A Characterization of Quantile Stable Matchings in Many-to-Many Markets

Abstract: We study two-sided many-to-many matching markets where agents' preferences satisfy strong substitutability and the law of aggregate demand (LAD). In this framework, the set of stable matchings forms a finite distributive lattice, and quantile stable matchings exist and satisfy the polarization of interests. Building on the cycle-reduction machinery of Bonifacio et al. (2022), we provide a purely combinatorial characterization of quantile stable matchings formulated in terms of preference cycles and their induced precedence order. Specifically, we define an order-theoretic counting function on cycles and prove that each quantile stable matching corresponds to the elimination of an endogenously determined closed set of cycles starting from the firm-optimal stable matching. This characterization extends the rotation-based framework of Cheng (2008) from one-to-one markets to many-to-many markets and bypasses the need for exhaustive outcome enumeration or partner sorting across the entire stable set.