Bisimulation Minimization of Tree Automata

We extend an algorithm by Paige and Tarjan that solves the coarsest stable refinement problem to the domain of trees. The algorithm is used to minimize non-deterministic tree automata (NTA) with respect to bisimulation. We show that our algorithm has an overall complexity of $O(\hat{r}m \log n)$, where $\hat{r}$ is the maximum rank of the input alphabet, m is the total size of the transition table, and n is the number of states.

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