On ET0L Systems with rank

摘要

The notion of an ET0L system with rank is defined. It naturally extends already studied notions of a D0L system with rank and of an ET0L system of finite index. It turns out that in this way one gets an infinite hierarchy of classes of languages (each one being a full AFL) within the class of ET0L languages. This hierarchy starts with the class of ET0L languages of finite index and it fills in the class of nonexpansive ET0L languages. Some other properties of the class of ET0L systems with rank are also studied.