Abstract
Graph-walking automata (GWA) analyze an input graph by moving between its nodes, following the edges. This paper investigates the effect of node-replacement graph homomorphisms on recognizability by these automata. The family of graph languages recognized by GWA is closed under inverse homomorphisms. The main result of this paper is that, for n-state automata operating on graphs with k labels of edge end-points, the inverse homomorphic images require GWA with \(kn+O(1)\) states in the worst case. The second result is that already for tree-walking automata, the family they recognize is not closed under injective homomorphisms; here the proof is based on a homomorphic characterization of regular tree languages.
This work was supported by the Ministry of Science and Higher Education of the Russian Federation, agreement 075-15-2019-1619.
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Martynova, O., Okhotin, A. (2022). Homomorphisms on Graph-Walking Automata. In: Caron, P., Mignot, L. (eds) Implementation and Application of Automata. CIAA 2022. Lecture Notes in Computer Science, vol 13266. Springer, Cham. https://doi.org/10.1007/978-3-031-07469-1_14
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