Summary
There is no algorithm for deciding whether two linear context-free grammars generate the same sentential forms. The equivalence problem for propagatingOL-systems is undecidable. The finiteness problem forOL-systems is decidable.SF-languages, i.e., languages which equal the set of sentential forms of a context-free grammar, possess some of the properties of context-free languages but their family is not closed under any of the ordinary operations.
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References
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Salomaa, A. On sentential forms of context-free grammars. Acta Informatica 2, 40–49 (1973). https://doi.org/10.1007/BF00571462
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DOI: https://doi.org/10.1007/BF00571462