@TechReport{MalerStaiger93,
  author =    "Oded Maler and Ludwig Staiger",
  title =     "On {S}yntactic {C}ongruences for omega-languages",
  institution = "RWTH Aachen",
  year =      "1993",
  number =    "AIB-13-1993",
  url =       "http://aib.informatik.rwth-aachen.de/1993/1993-13.ps.gz",
}