Pattern Ambiguities for Pure Context—Free Grammars

Abstract

We consider here some special forms of ambiguity for pure context-free grammars, namely pattern avoiding ambiguity, pattern preserving ambiguity, pattern ambiguity, and grammar avoiding ambiguity. The first two properties are undecidable for arbitrary pure context-free grammars, and in a particular but general enough case we can effectively decide whether or not a pure context-free grammar is pattern preserving ambiguous.