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Partial sums of Taylor series on a circle

E. S. Katsoprinakis, V. N. Nestoridis (1989)

Annales de l'institut Fourier

We characterize the power series n = 0 c n z n with the geometric property that, for sufficiently many points z , | z | = 1 , a circle C ( z ) contains infinitely many partial sums. We show that n = 0 c n z n is a rational function of special type; more precisely, there are t and n 0 , such that, the sequence c n e int , n n 0 , is periodic. This result answers in the affirmative a question of J.-P. Kahane and furnishes stronger versions of the main results of [Katsoprinakis, Arkiv for Matematik]. We are led to consider special families of circles C ( z ) with...

Periodic quasiregular mappings of finite order.

David Drasin, Swati Sastry (2003)

Revista Matemática Iberoamericana

The authors construct a periodic quasiregular function of any finite order p, 1 < p < infinity. This completes earlier work of O. Martio and U. Srebro.

Pervasive algebras on planar compacts

Jan Čerych (1999)

Commentationes Mathematicae Universitatis Carolinae

We characterize compact sets X in the Riemann sphere 𝕊 not separating 𝕊 for which the algebra A ( X ) of all functions continuous on 𝕊 and holomorphic on 𝕊 X , restricted to the set X , is pervasive on X .

Pick-Nevanlinna interpolation on finitely-connected domains

Stephen Fisher (1992)

Studia Mathematica

Let Ω be a domain in the complex plane bounded by m+1 disjoint, analytic simple closed curves and let z 0 , . . . , z n be n+1 distinct points in Ω. We show that for each (n+1)-tuple ( w 0 , . . . , w n ) of complex numbers, there is a unique analytic function B such that: (a) B is continuous on the closure of Ω and has constant modulus on each component of the boundary of Ω; (b) B has n or fewer zeros in Ω; and (c) B ( z j ) = w j , 0 ≤ j ≤ n.

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