Abstract
Higher-order grammars have been extensively studied in 1980’s and interests in them have revived recently in the context of higher-order model checking and program verification, where higherorder grammars are used as models of higher-order functional programs. A lot of theoretical questions remain open, however, for unsafe higherorder grammars (grammars without the so-called safety condition). In this paper, we show that any tree languages generated by order-2 unsafe grammars are context-sensitive. This also implies that any unsafe order-3 word languages are context-sensitive. The proof involves novel technique based on typed lambda-calculus, such as type-based grammar transformation.
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Kobayashi, N., Inaba, K., Tsukada, T. (2014). Unsafe Order-2 Tree Languages Are Context-Sensitive. In: Muscholl, A. (eds) Foundations of Software Science and Computation Structures. FoSSaCS 2014. Lecture Notes in Computer Science, vol 8412. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-54830-7_10
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DOI: https://doi.org/10.1007/978-3-642-54830-7_10
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