A Note on the Emptiness of Intersection Problem for Left Szilard Languages

Abstract

As left Szilard languages form a subclass of simple deterministiclanguages and even a subclass of super-deterministic languages, weknow that their equivalence problem is decidable. In this note weshow that their emptiness of intersection problem is undecidable.The proof follows the lines of the correponding proof for simpledeterministic languages, but some technical tricks are needed. Thisresult sharpens the borderline between decidable and undecidableproblems in formal language theory.