@inproceedings(nguyen994b, 
  author    = {Linh Anh Nguyen},
  title     = {A New Space Bound for the Modal Logics 
               {K4}, {KD4} and {S4}},
  booktitle = {Proceedings of MFCS'99, LNCS 1672}, 
  editor    = {M. Kutylowski and L. Pacholski}, 
  pages     = {321-331}, 
  publisher = {Springer},
  year      = 1999)