@InProceedings{alti:cmcs01,
  author =       {Jeremy Gibbons and Graham Hutton and Thorsten Altenkirch},
  title =        {When is a function a fold or an unfold? },
  booktitle =    {Proceedings of the 4th International Workshop on Coalgebraic Methods in Computer Science},
  year =         {2001},
  volume =       {44.1},
  series =       {Electronic Notes in Theoretical Computer Science},
}