On Nilpotent Languages and Their Characterization by Regular Expressions

György Gyurica
2009 Acta Cybernetica  
Tree languages recognized by deterministic root-to-frontier recognizers are also called DR-languages. The concept of generalized R-chain languages was introduced by the author in his paper On monotone languages and their characterization by regular expressions (Acta Cybernetica, 18 (2007) , 117-134.) and it has turned out that the monotone DR-languages are exactly those languages that can be given by generalized R-chain languages. In this paper we give a similar characterization for nilpotent
more » ... ion for nilpotent DR-languages by means of plain R-chain languages. Also a regular expression based characterization is given for nilpotent string languages.
doi:10.14232/actacyb.19.1.2009.15 fatcat:ltt2amld75cppeky6kxfxqhrby