S. Maity, Y. Akhtar, R. C. Chandrasekharan, and C. J. Colbourn, Improved Strength Four Covering Arrays with Three Symbols, Graphs and Combinatorics, 34 (1), 223-239, 2018.
S. Maity, Y. Akhtar, R. C. Chandrasekharan, and C. J. Colbourn, Improved Strength Four Covering Arrays with Three Symbols, Graphs and Combinatorics, 34 (1), 223-239, 2018.