@article{BenhammadiNicolasSchaub1998,
  author    = {Benhammadi, Farid and Nicolas, Pascal and Schaub, Torsten H.},
  title     = {Extension calculus and query answering in prioritized default logic},
  isbn      = {3-540-64993-X},
  year      = {1998},
  language  = {en}
}
@article{BenhammadiNicolasSchaub1998,
  author    = {Benhammadi, Farid and Nicolas, Pascal and Schaub, Torsten H.},
  title     = {Extension calculus and query answering in prioritized default logic},
  isbn      = {3-540- 64993-X},
  year      = {1998},
  language  = {en}
}
@article{NicolasSchaub1998,
  author    = {Nicolas, Pascal and Schaub, Torsten H.},
  title     = {The XRay system : an implementation platform for local query-answering in default logics},
  isbn      = {3-540-65312-0},
  year      = {1998},
  language  = {en}
}
@article{NicolasSchaub1998,
  author    = {Nicolas, Pascal and Schaub, Torsten H.},
  title     = {Un cadre g{\´e}n{\´e}ral pour l'interrogation automatique en logiques des d{\´e}fauts},
  year      = {1998},
  language  = {fr}
}