On Even Linear Indexed Languages with a Reduction to the Learning of Context-Free Languages

Abstract

This paper presents a restricted form of linear indexed grammars, called even linear indexed grammars, which yield the even linear indexed languages. These languages properly contain the context-free languages and are contained in the set of linear indexed languages. We show that several patterns found in natural languages are also generated by these grammars, including crossing dependencies, copying, and multiple agreements. We discuss the learning problem for even linear indexed languages and show that it is reducible to that of the context-free languages. The closure properties for this class of languages are also presented.