Equal matrix languages and Kleene closure

Abstract

It is shown that the family of equal matrix languages (EML) which intersects the family of context-sensitive and context-free languages is not closed under Kleene closure, intersection and complementation. The family of bounded EML whose generative power lies between that of bounded context-sensitive languages and bounded context-free languages is shown to be a class of unambiguous languages. Operations that preserve unambiguity and certain decidability questions are discussed.