On ET0L Systems with Rank

Abstract The notion of an ET 0 L system with rank is defined. It naturally extends already studied notions of a D 0 L system with rank and of an ET 0 L 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 ET 0 L languages. This hierarchy starts with the class of ET 0 L languages of finite index and it fills in the class of nonexpansive ET 0 L languages. Some other properties of the class of ET 0 L systems with rank are also studied.