APPLIED MATHEMATICS LETTERS, vol. 22, no. 2, page. 159 - 162, 2009-02
APPLIED MATHEMATICS LETTERS, vol. 21, no. 12, page. 1306 - 1309, 2008-12
SIAM JOURNAL ON DISCRETE MATHEMATICS, vol. 25, no. 4, page. 1902 - 1919, 2011-12
EUROPEAN JOURNAL OF COMBINATORICS, vol. 29, no. 7, page. 1617 - 1633, 2008-10
APPLIED MATHEMATICS LETTERS, vol. 21, no. 6, page. 545 - 548, 2008-06