INFORMATION PROCESSING LETTERS, vol. 110, no. 1, page. 24 - 29, 2009-12-01
INFORMATION PROCESSING LETTERS, vol. 109, no. 12, page. 608 - 610, 2009-05-31
INFORMATION PROCESSING LETTERS, vol. 109, no. 16, page. 913 - 917, 2009-07-31