Ferreira, M. R. P., L. F. D. Santos, A. J. M. Traina, I. Dias, R. Chbeir, and C. Traina Jr. “Algebraic Properties to Optimize KNN Queries”. Journal of Information and Data Management, vol. 2, no. 3, Oct. 2011, p. 385, doi:10.5753/jidm.2011.1416.