Vinh, Trịnh Đình, and Vũ Đức Thi. “Cover of the Set of Functional Dependencies and Quasinorms in Database Model If Block”. <i>Journal of Computer Science and Cybernetics</i>, vol. 26, no. 4, Apr. 2012, pp. 312-20, doi:10.15625/1813-9663/26/4/505.