Finite Blaschke products of contractions
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Hwa-Long Gau; Pei Yuan Wu
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Article
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2003
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Elsevier Science
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English
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Let A be a contraction on Hilbert space H and ฯ a finite Blaschke product. In this paper, we consider the problem when the norm of ฯ(A) is equal to 1. We show that (1) ฯ(A) = 1 if and only if A k = 1, where k is the number of zeros of ฯ counting multiplicity, and (2) if H is finite-dimensional and A