References
- Rosenkrantz , D.J. 1969 . Programmed grammars and classes for formal languages . JACM , 16 ( 1 ) : 107 – 131 .
- Rosenkrantz D.J. 1972 private communication
- Wood D. Bicoloured digraph grammar systems Review francaise d'Informatique et de Recherche Operationelle 1973 to appear