Merging Two Hierarchies of External Contextual Grammars with Subregular Selection

Merging two Hierarchies of Internal Contextual Grammars with Subregular Selection

“…A recent survey can be found in [27] which presents for each type of contextual grammars (external and internal ones) two hierarchies, one based on selection languages defined by structural properties (finite, monoidal, nilpotent, combinational, definite, ordered, non-counting, power-separating, suffixclosed, commutative, circular, or union-free languages), the other one based on selection languages defined by resources (number of non-terminal symbols, production rules, or states needed for generating or accepting them). In [28], the language families of these hierarchies for external contextual grammars were compared and the hierarchies merged. In the present paper, we compare the language families of these hierarchies for internal contextual grammars and merge the hierarchies.…”