[1] G. T. Herman G. Rozenberg:
Developmental Systems and Languages. North-Holland Publishing Company, Amsterdam - Oxford, American Elsevier Publishing Company, Inc., New York 1975.
MR 0495247
[2] J. Král:
A Modification of a Substitution Theorem and Some Necessary and Sufficient Conditions for Sets to Be Context-Free. Mathematical Systems Theory 4 (1970), 2, 129-139.
MR 0272566
[3] G. Rozenberg P. G. Doucet:
On 0L-Languages. Informations and Control 19 (1971), 4, 302-318.
MR 0317597
[5] A. Salomaa:
On Sentential Forms of Context-Free Grammars. Acta Informatica 2 (1973), 1, 40-49.
MR 0324962 |
Zbl 0264.68029