@inbook{BUT191802,
  author="Alexandr {Meduna}",
  title="On the Number of Nonterminals in Matrix Grammars with Leftmost Derivations",
  booktitle="New Trends in Formal Languages: Control, Cooperation, and Combinatorics",
  year="1997",
  publisher="Springer Verlag",
  address="New York",
  pages="27--39"
}