@TechReport{MallenDeFrutosEscrig90,
  author =   {Ortega Mallen, Y. and de Frutos Escrig, D.},
  title =     "A Complete {P}roof {S}ystem for {T}imed {O}bservations",
  institution = "RWTH Aachen",
  year =      "1990",
  number =    "AIB-20-1990",
  url =       "http://aib.informatik.rwth-aachen.de/1990/1990-20.ps.gz",
}