Abstract

We develop a necessary condition for ET0L languages inspired by Ogden's Lemma. Besides being useful for proving that individual languages are not ET0L languages, this result also gives an alternative proof of Ehrenfeucht and Rozenberg's theorem about rare and nonfrequent symbols in ET0L languages.

Full Text
Published version (Free)

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call