V. DeBellis. Discrete Mathematics in the Schools, volume 36 of DIMACS Series in Discrete Mathematics and Theoretical Computer Science, page 187-201. DIMACS/AMS, (1992)
J. Rosenstein, and V. DeBellis. Discrete Mathematics in the Schools, volume 36 of DIMACS Series in Discrete Mathematics and Theoretical Computer Science, page 415-431. DIMACS/AMS, (1992)