On the recognition problem for virtually special cube complexes

Martin R. Bridson and Henry Wilton

We address the question of whether the property of being virtually special (in
the sense of Haglund and Wise) is algorithmically decidable for finite, non-positively
curved cube complexes. Our main theorem shows that it cannot be decided locally,
i.e. by examining one hyperplane at a time. Specifically, we prove that there does not
exist an algorithm that, given a compact non-positively squared 2-complex X and a
hyperplane H in X can decide whether or not there is a finite-sheeted cover of X in
which no lift of H self-osculates.