Selected references
- David G. Cantor. On the ambiguity problem of Backus systems. Journal of the ACM, 9(4):477-479, October 1962.
- Noam Chomsky. On certain formal properties of grammars. Information and Control, 2(2):137-167, June 1959.
- Seymour Ginsburg and H. Gordon Rice. Two families of languages related to ALGOL. Journal of the ACM, 9(3):350-371, July 1962.