Each regular code is included in a maximal regular code

Ehrenfeucht, A.; Rozenberg, G.

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications, Volume 20 (1986) p. 89-96

Coordinated pair systems ; part I : Dyck works and classical pumping

Ehrenfeucht, A.; Hoogeboom, H. J.; Rozenberg, G.

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications, Volume 20 (1986) p. 405-424

Coordinated pair systems ; part II : sparse structure of Dyck words and Ogden's lemma

Ehrenfeucht, A.; Hoogeboom, H. J.; Rozenberg, G.

RAIRO - Theoretical Informatics and Applications - Informatique Théorique et Applications, Volume 20 (1986) p. 425-439