@Article{PittsAM:newaas-jv,
  author =	 {M. J. Gabbay and A. M. Pitts},
  title =	 {A New Approach to Abstract Syntax with Variable
                  Binding},
  journal =	 {Formal Aspects of Computing},
  year =	 2001,
  volume =	 13,
  pages =	 {341--363}
}