On the closedness of nilpotent DR tree languages under Boolean operations. - Ferenc Gécseg; György Gyurica (Acta Cybern., 2006)

On monotone languages and their characterization by regular expressions. - György Gyurica (Acta Cybern., 2007)

On Nilpotent Languages and Their Characterization by Regular Expressions. - György Gyurica (Acta Cybern., 2009)