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Collapsible Pushdown Graphs of Level 2 are Tree-Automatic (1303.2453v2)
Published 11 Mar 2013 in cs.LO, cs.FL, and math.LO
Abstract: We show that graphs generated by collapsible pushdown systems of level 2 are tree-automatic. Even if we allow epsilon-contractions and reachability predicates (with regular constraints) for pairs of configurations, the structures remain tree-automatic whence their first-order logic theories are decidable. As a corollary we obtain the tree-automaticity of the second level of the Caucal-hierarchy.