Structural Equivalence and ETOL grammars

@inproceedings{Salomaa1993StructuralEA,
  title={Structural Equivalence and ETOL grammars},
  author={Kai Salomaa and Derick Wood and Sheng Yu},
  year={1993}
}
For a given context-sensitive grammar G we construct ET0L grammars G1 and G2 that are structurally equivalent if and only if the language generated by G is empty, which implies that structural equivalence is undecidable for ET0L grammars. This is in contrast to the decidability result for the E0L case. In fact, we show that structural equivalence is undecidable for propagating ET0L grammars even when the number of tables is restricted to be at most two. A stronger notion of equivalence that… 
Complexity of E0L Structural Equivalence
We show that the EOL structural equivalence problem is logspace hard for deterministic exponential time. Also, we show that this question can be solved in linear space by a synchronized alternating