J. Korean Math. Soc. 2004; 41(1): 65-76
Printed January 1, 2004
Copyright © The Korean Mathematical Society.
Richard Aron and Dinesh Markose
Kent State University, Cambridge University
An entire function $f \in {\mathcal H}(\mathbb{C})$ is called universal with respect to translations if for any $g \in {\mathcal H}(\mathbb{C}), R > 0,$ and $\epsilon > 0,$ there is $n \in \mathbb{N}$ such that $|f(z+n) - g(z)| < \epsilon$ whenever $|z| \leq \ $R. Similarly, it is universal with respect to differentiation if for any $g,R,$ and $\epsilon,$ there is $n$ such that $|f^{(n)}(z) - g(z)| < \epsilon$ for $|z| \leq$ R. In this note, we review G. MacLane's proof of the existence of universal functions with respect to differentiation, and we give a simplified proof of G. D. Birkhoff's theorem showing the existence of universal functions with respect to translation. We also discuss Godefroy and Shapiro's extension of these results to convolution operators as well as some new, related results and problems.
Keywords: hypercyclic, analytic functions, convolution operators
MSC numbers: Primary 47A16, 32DXX; Secondary 46B37
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