@article{smith-johnson-2007-weighted,
    title = "Weighted and Probabilistic Context-Free Grammars Are Equally Expressive",
    author = "Smith, Noah A.  and
      Johnson, Mark",
    journal = "Computational Linguistics",
    volume = "33",
    number = "4",
    year = "2007",
    url = "https://preview.aclanthology.org/fix-sig-urls/J07-4003/",
    doi = "10.1162/coli.2007.33.4.477",
    pages = "477--491"
}