Which Linear-fractional Composition Operators Are Essentially Normal?
نویسندگان
چکیده
We characterize the essentially normal composition operators induced on the Hardy space H2 by linear fractional maps; they are either compact, normal, or (the nontrivial case) induced by parabolic non-automorphisms. These parabolic maps induce the first known examples of nontrivially essentially normal composition operators. In addition we characterize those linearfractionally induced composition operators on H2 that are essentially selfadjoint, and present a number of results for composition operators induced by maps that are not linear fractional.
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