Abstract
Recent work by Knapik, NiwiĆski and Urzyczyn (in FOSSACS 2002) has revived interest in the connexions between higher-order grammars and higher-order pushdown automata. Both devices can be viewed as definitions for term trees as well as string languages. In the latter setting we recall the extensive study by Damm (1982), and Damm and Goerdt (1986). There it was shown that a language is accepted by a level-n pushdown automaton if and only if the language is generated by a safe level-n grammar. We show that at level 2 the safety assumption may be removed. It follows that there are no inherently unsafe string languages at level 2.
This is an extended abstract of a longer paper [2] complete with proofs, which is downloadable from the authorsâ web pages.
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Aehlig, K., de Miranda, J.G., Ong, C.H.L. (2005). Safety Is not a Restriction at Level 2 for String Languages. In: Sassone, V. (eds) Foundations of Software Science and Computational Structures. FoSSaCS 2005. Lecture Notes in Computer Science, vol 3441. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-31982-5_31
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DOI: https://doi.org/10.1007/978-3-540-31982-5_31
Publisher Name: Springer, Berlin, Heidelberg
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