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Published online by Cambridge University Press: 17 April 2009
We give sufficient and necessary conditions for simple modules of the quantum group or the quantum enveloping algebra Uq(g) to have weight space decompositions, where g is a semisimple Lie algebra and q is a nonzero complex number. We show that
(i) if q is a root of unity, any simple module of Uq(g) is finite dimensional, and hence is a weight module;
(ii) if q is generic, that is, not a root of unity, then there are simple modules of Uq(g) which do not have weight space decompositions.
Also the group of units of Uq(g) is found.