Patel-Schneider, P. F., B. Owsnicki-Klewe, A. Kobsa, N. Guarino, R. MacGregor, W. S. Mark, D. L. McGuinness, B. Nebel, A. Schmiedel, and J. Yen. “Term Subsumption Languages in Knowledge Representation”. AI Magazine, vol. 11, no. 2, June 1990, p. 16, doi:10.1609/aimag.v11i2.835.