On Etol Systems with Finite Tree-Rank
A. Ehrenfeucht, Grzegorz Rozenberg, Dirk Vermeir · SIAM Journal on Computing · 1981
This paper studies an extension of the notion of a finite index ETOL system. It turns out that by setting some quite natural restrictions on the set of bare derivation trees of an ETOL system (that is derivation trees stripped of labels) one can characterize languages of finite rank. Several properties of the new class of ETOL systems are investigated; in particular their relationship to ETOL systems of finite rank and ETOL systems of finite index is investigated.