The Emptiness Problem for Tree Automata with at Least One Disequality Constraint is NP-hard
arXiv:1412.0839
Abstract
The model of tree automata with equality and disequality constraints was introduced in 2007 by Filiot, Talbot and Tison. In this paper we show that if there is at least one disequality constraint, the emptiness problem is NP-hard.