Submitted on: 22 March 1999.
Revised on: 22 April 1999.
Accepted on: 07 May 1999.
Research in Mathematics---TAYLOR & FRANCIS LTD
http://reply.papertrans.cn/3/265/26418/26418-32.png
http://reply.papertrans.cn/3/265/26418/26418-33.png
http://reply.papertrans.cn/3/265/26418/26418-34.png
http://reply.papertrans.cn/3/265/26418/26418-35.png
Submitted on: 04 July 2008.
Revised on: 26 July 2008.
Accepted on: 20 August 2008.
Research in Mathematics---TAYLOR & FRANCIS LTD