Dense Hierarchies of Grammatical Families
Hermann A. Maurer, A. Salomaa, D. Wood · Journal of the ACM · 1982
A technique ts presented for constructing dense hierarchies of grammatical subfamthes of context-free languages The question of "where" such dense hierarchies may lie is also investigated Infinite hierarchies of successors are studied.The major open problems concern questions deahng with fimte grammar forms Categories and SubJect Descriptors.F 4 3 ]