Composition Operators on Small Spaces |
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Authors: | Boo Rim Choe Hyungwoon Koo Wayne Smith |
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Institution: | (1) Department of Mathematics, Korea University, Seoul, 136-701, Korea;(2) Department of Mathematics, University of Hawaii, Honolulu, 96822, Hawaii, USA |
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Abstract: | We show that if a small holomorphic Sobolev space on the unit disk is not just small but very small, then a trivial necessary
condition is also sufficient for a composition operator to be bounded. A similar result for holomorphic Lipschitz spaces is
also obtained. These results may be viewed as boundedness analogues of Shapiro’s theorem concerning compact composition operators
on small spaces. We also prove the converse of Shapiro’s theorem if the symbol function is already contained in the space
under consideration. In the course of the proofs we characterize the bounded composition operators on the Zygmund class. Also,
as a by-product of our arguments, we show that small holomorphic Sobolev spaces are algebras. |
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Keywords: | Primary 47B33 Secondary 30D55 46E15 |
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