On ground word problem of term equation systems

We give semi-decision procedures for the ground word problem of variable preserving term equation systems and term equation systems. They are natural improvements of two well known trivial semi-decision procedures. We show the correctness of our procedures

Top-down tree transducers with two-way tree walking look-ahead

AbstractWe consider top-down tree transducers with deterministic, nondeterministic and universal two-way tree walking look-ahead and compare the transformational powers of their deterministic and strongly deterministic versions by giving the inclusion diagram of the induced tree transformation classes. We also study the closure properties of these transformation classes with respect to composition

Storage-to-tree transducers with look-ahead

AbstractWe generalize Engelfriet's decomposition result stating that the class of transformations induced by top–down tree transducers with regular look-ahead is equal to the composition of the class of top–down tree transformations and the class of linear tree homomorphisms. Replacing the input trees with an arbitrary storage type, the top–down tree transducers are turned into regular storage-to-tree transducers. We show that the class of transformations induced by regular storage-to-tree transducers with positive look-ahead is equal to the composition of the class of transformations induced by regular storage-to-tree transducers with the class of linear tree homomorphisms. We also show that the classes of transformations induced by both IO and OI context-free storage-to-tree transducers are closed under positive look-ahead, and are closed under composition with linear tree homomorphisms

One-Pass Reductions

We study OI and IO one-pass reduction sequences with term rewrite systems. We present second order decidability and undecidability results on recognizable tree languages and one-pass reductions. For left-linear TRSs, the second order OI inclusion problem and the second order OI reachability problem are decidable, the second order OI joinability problem is undecidable. For right-linear TRSs, the second order common IO ancestor problem is undecidable