On Normal Forms and Erasing Rules in Path Controlled Grammars

This paper discusses path controlled grammars—context-free gram- mars with a root-to-leaf path in their derivation trees restricted by a control language. First, it investigates the impact of erasing rules on the generative power of path controlled grammars. Then, it establishes two Chomsky-like normal forms for path controlled grammars—the first allows unit rules, the second allows just one erasing rule

Tree-controlled grammars with restrictions placed upon cuts and paths

summary:First, this paper discusses tree-controlled grammars with root-to-leaf derivation-tree paths restricted by control languages. It demonstrates that if the control languages are regular, these grammars generate the family of context-free languages. Then, in a similar way, the paper introduces tree-controlled grammars with derivation-tree cuts restricted by control languages. It proves that if the cuts are restricted by regular languages, these grammars generate the family of recursively enumerable languages. In addition, it places a binary-relation-based restriction upon these grammars and demonstrate that this additional restriction does not affect the generative power of these grammars