JOURNAL OF ALGEBRAIC COMBINATORICS, vol. 13, no. 1, page. 5 - 13, 2001-01
PROCEEDINGS OF THE AMERICAN MATHEMATICAL SOCIETY, vol. 130, no. 11, page. 3125 - 3131, 2002-01
DISCRETE MATHEMATICS, vol. 270, no. 1-3, page. 43 - 60, 2003-08-28
DISCRETE MATHEMATICS, vol. 282, no. 1-3, page. 81 - 87, 2004-05-06