@inproceedings{kugel-1965-sets,
    title = "Sets of Grammars Between Context-Free and Context-Sensitive",
    author = "Kugel, Peter",
    booktitle = "COLING 1965",
    year = "1965",
    url = "https://preview.aclanthology.org/jlcl-multiple-ingestion/C65-1016/"
}