@article{cj00-02,
  author={Manindra Agrawal, Eric Allender,Samir Datta, Heribert Vollmer, Klaus W. Wagner}
  title={Characterizing Small Depth and Small Space Classes\\
by Operators of Higher Types}
  journal={Chicago Journal of Theoretical Computer Science},
  volume={2000},
  number={2},
  publisher={MIT Press},
  month={August},
  year={2000}
}