On Monotone Automata and Monotone Languages
Ferenc Gécseg, Balázs Imreh · Journal of automata, languages and combinatorics · 2002
In this paper monotone string and monotone tree languages are studied. For the string case, the monotone languages are characterized by means of regular expressions and syntactic monoids. Tree languages recognized by monotone frontier-to-root and monotone root-to-frontier recognizers are also characterized by syntactic monoids