A Generalization of Ogden's Lemma
Christopher D. Bader, Arnaldo Moura · Journal of the ACM · 1982
Excluded positions" are incorporated into a modified form of Ogden's lemma, and a language satisfying the latter, which the authors' generalized lemma can show fails to be context-free, is presented.It is also shown that in a fairly general sense there ts no function relating the number of distinguished and excluded posnions which would allow the authors' Iteration lemma to characterize the context-free languages.Categones and SubJect Descriptors' F 4.2