Uniform approximation of Bloch functions and the boundedness of the   integration operator on $H^\infty$
  We obtain a necessary and sufficient condition for the operator of integration to be bounded on $H^\infty$ in a simply connected domain. The main ingredient of the proof is a new result on uniform approximation of Bloch functions. This gives a full characterization of symbols of certain Volterra operators that act on bounded analytic functions in the disc if the symbol is assumed to be univalent. Without this assumption the answer is not known, and as the example at the end of the paper shows, the natural answer is definitely false. 
Wayne Smith, Dmitriy M. Stolyarov, Alexander Volberg
math.CV math.CA math.FA