@inproceedings{melcuk-gladky-1969-tree,
    title = "Tree Grammars (= {{\ensuremath{\Delta}}}-Grammars)",
    author = "Mel{'}{\v{c}}uk, I. A.  and
      Gladky, A. V.",
    booktitle = "{I}nternational {C}onference on {C}omputational {L}inguistics {COLING} 1969: Preprint No. 1",
    month = sep,
    year = "1969",
    address = {S{\r{a}}nga S{\"a}by, Sweden},
    url = "https://preview.aclanthology.org/fix-sig-urls/C69-0101/"
}