@InProceedings{KulasMpurpe,
  author =      {M.~Kula\v{s}},
  title =       {Pure {P}rolog Execution in 21 Rules},
  booktitle =   {Proc. of the 5th Workshop on Rule-Based Constraint Reasoning and Programming (RCoRP'03), Kinsale},
  year =        {2003},
  month =       {September},
url={ http://www.univ-orleans.fr/SCIENCES/LIFO/Members/lallouet/rcorp03 },
abstract={ A simple mathematical definition of the 4-port model for pure 
Prolog is given. The model combines the intuition of ports with a compact
representation of execution state. Forward and backward derivation
steps are possible. The model satisfies a modularity claim, making it
suitable for formal reasoning. } }