Context-free multilanguages
<|reference_start|>Context-free multilanguages: This article is a sketch of ideas that were once intended to appear in the author's famous series, "The Art of Computer Programming". He generalizes the notion of a context-free language from a set to a multiset of words over an alphabet. The idea is to keep track of the number of ways to parse a string. For example, "fruit flies like a banana" can famously be parsed in two ways; analogous examples in the setting of programming languages may yet be important in the future.   The treatment is informal but essentially rigorous.<|reference_end|>
@article{knuth1991context-free,
    title={Context-free multilanguages},
    author={Donald E. Knuth},
    journal={Theoretical Studies in Computer Science, Ginsburg Festschrift},
    year={1991},
    number={Knuth migration 11/2004 1991},
    archivePrefix={arXiv},
    eprint={cs/9301115},
    primaryClass={cs.DS}
}