Complexity of Conjugacy, Factoring and Embedding for Countable Sofic   Shifts of Rank 2
  In this article, we study countable sofic shifts of Cantor-Bendixson rank at most 2. We prove that their conjugacy problem is complete for GI, the complexity class of graph isomorphism, and that the existence problems of block maps, factor maps and embeddings are NP-complete. 
Ville Salo and Ilkka T\"orm\"a
math.DS cs.CC cs.FL