@inproceedings{joshi-1969-properties,
    title = "Properties of Formal Grammars With Mixed Type of Rules and Their Linguistic Relevance",
    author = "Joshi, Aravind K.",
    booktitle = "{I}nternational {C}onference on {C}omputational {L}inguistics {COLING} 1969: Preprint No. 47",
    month = sep,
    year = "1969",
    address = {S{\r{a}}nga S{\"a}by, Sweden},
    url = "https://preview.aclanthology.org/landing_page/C69-4701/"
}