Existential length universality

  title={Existential length universality},
  author={Pawel Gawrychowski and Narad Rampersad and Jeffrey Shallit and Marek Szykula},
We study the following natural variation on the classical universality problem: given an automaton M of some type (DFA/NFA/PDA), does there exist an integer l ≥ 0 such that Σl ⊆ L(M)? The case of an NFA was an open problem since 2009. Here, using a novel and deep construction, we prove that the problem is NEXPTIME-complete, and the smallest such l can be… CONTINUE READING