A Birkhoff theorem for Riemann surfaces

Abstract

A classical theorem of Birkhoff asserts that there exists an entire function f such that the sequence of function {/(z + n)}n≥o is dense in the space of entire functions. In this paper we give sufficient conditions on a Riemann surface R and on a given sequence {φn}n≥o of holomorphic self-mappings of R such that there exists a holomorphic function f on R such that {f o φn}n≥0 is dense in the space of holomorphic functions on R. The necessity of these conditions is examined. In particular, we characterize the Riemann surfaces R and the sequences {φn}n≥0 of automorphisms of R. for which there exists a holomorphic function f on R with the property that the sequence {f o φn] n≥o is dense in the space of the holomorphic functions on R.