@Misc{		  dix91normal,
  author	= {J\"{u}rgen Dix},
  title		= {{N}ormal {L}ogic {P}rograms and {C}umulativity},
  howpublished	= {9 th International Congress of Logic, Methodology and
		  Philosophy of Science, Uppsala, Sweden},
  month		= {August},
  year		= {1991}
}