We study a generalization of Shapley-Scarfs [Journal of Mathematical Econom
ics 1 (1974) 23-37] economy in which multiple types of indivisible goods ar
e traded, We show that many of the distinctive results from the Shapley-Sca
rf economy do not carry over to this model, even if agents' preferences are
strict and can be represented by additively separable utility functions. T
he core may be empty. The strict core, if nonempty, may be multi-valued, an
d might not coincide with the set of competitive allocations, Furthermore,
there is no Pareto efficient, individually rational, and strategy-proof soc
ial choice rule. We also show that the core may be empty in the class of ec
onomies with a single type of indivisible good and agents consuming multipl
e units, even if no complementarity exists among the goods. (C) 2001 Elsevi
er Science B.V. All rights reserved.