  We propose a pseudo-market solution to resource allocation problems subject
to constraints. Our treatment of constraints is general: including
bihierarchical constraints due to considerations of diversity in school choice,
or scheduling in course allocation; and other forms of constraints needed to
model, for example, the market for roommates, and combinatorial assignment
problems. Constraints give rise to pecuniary externalities, which are
internalized via prices. Agents pay to the extent that their purchases affect
the value of relevant constraints at equilibrium prices. The result is a
constrained efficient market equilibrium outcome. The outcome is fair whenever
the constraints do not single out individual agents. Our result can be extended
to economies with endowments, and address participation constraints.
