  In the theory of two-sided matching markets there are two well-known models:
the marriage model (where no money is involved) and the assignment model (where
payments are involved). Roth and Sotomayor (1990) asked for an explanation for
the similarities in behavior between those two models. We address this question
by introducing a common generalization that preserves the two important
features: the existence of a stable outcome and the lattice property of the set
of stable outcomes.
