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The commutant of rationally cyclic subnormal operators and rational approximation
Authors:James Zhijian Qiu
Institution:(1) Pure Atria Corporation, McLean, Virginia, USA;(2) 11106-4c, Cavalier CT, 22030 Fairfax, VA, USA
Abstract:Let OHgr denote the set of analytic bounded point evaluations forR q (K, mgr). Assume that 
$$\bar \Omega  = K$$
. In this paper, we first show that if OHgr is a finitely connected domain and if the evaluation map fromR q (K, mgr)pcyL infin(mgr) toH infin(OHgr) is surjective, then mgr|partOHgr is absolutely continuous with respect to harmonic measure for OHgr. This generalizes Olin and Yang's corresponding result for polynomials and the proof we present here is simpler. We also provide an example that shows this absolute continuity property fails in general when OHgr is an infinitely connected domain. In the second part, we then offer a solution to a problem of Conway and Elias.
Keywords:Primary 47B20  Secondary 30H05  30E10  46E15
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