Submitted on: 22 June 2002.
Revised on: 01 October 2002.
Accepted on: 12 November 2002.
___________________DISCRETE APPLIED MATHEMATICS---ELSEVIER
http://reply.papertrans.cn/1/76/7542/7542-22.png
http://reply.papertrans.cn/1/76/7542/7542-23.png
http://reply.papertrans.cn/1/76/7542/7542-24.png
http://reply.papertrans.cn/1/76/7542/7542-25.png
Submitted on: 28 July 2012.
Revised on: 28 September 2012.
Accepted on: 05 November 2012.
___________________DISCRETE APPLIED MATHEMATICS---ELSEVIER
http://reply.papertrans.cn/1/76/7542/7542-27.png
Submitted on: 13 July 2020.
Revised on: 16 September 2020.
Accepted on: 29 October 2020.
___________________DISCRETE APPLIED MATHEMATICS---ELSEVIER
Submitted on: 13 June 2002.
Revised on: 05 July 2002.
Accepted on: 06 August 2002.
___________________DISCRETE APPLIED MATHEMATICS---ELSEVIER
http://reply.papertrans.cn/1/76/7542/7542-30.png