JOURNAL OF PURE AND APPLIED ALGEBRA, vol. 146, no. 3, page. 283 - 290, 2000-03-02
COMMUNICATIONS IN ALGEBRA, vol. 28, no. 5, page. 2533 - 2542, 2000-01
HOUSTON JOURNAL OF MATHEMATICS, vol. 26, no. 1, page. 67 - 81, 2000-01