  In discrete matching markets, substitutes and complements can be
unidirectional between two groups of workers when members of one group are more
important or competent than those of the other group for firms. We show that a
stable matching exists and can be found by a two-stage Deferred Acceptance
mechanism when firms' preferences satisfy a unidirectional substitutes and
complements condition. This result applies to both firm-worker matching and
controlled school choice. Under the framework of matching with continuous
monetary transfers and quasi-linear utilities, we show that substitutes and
complements are bidirectional for a pair of workers.
