@INPROCEEDINGS{BHS93,
  AUTHOR    = {Bernhard Beckert and Reiner H\"{a}hnle and 
               Peter H. Schmitt},
  BOOKTITLE = {Proceedings of the third {K}urt {G}\"{o}del Colloquium 
               {KGC}'93, Brno, Czech Republic},
  EDITOR    = {Georg Gottlob and Alexander Leitsch and Daniele Mundici},
  MONTH     = {Aug},
  PAGES     = {108--119},
  PUBLISHER = {Springer {LNCS} 713},
  TITLE     = {The {\em even more} liberalized $\delta$-rule in free variable 
               semantic tableaux},
  YEAR               = {1993}
}