Characterization of context-free grammatical families
Armin Bernd Cremers, Seymour Ginsburg · 1974
Two characterization theorems for the class of context-free grammatical families are given. The characterizations are expressed in terms of the family of regular sets, the family of linear sets, and the following language-family operators: union, concatenation, the full semi-AFL operator, the full AFL operator, and a new ternary substitution operator.