http://reply.papertrans.cn/1/28/2800/2800-31.png
http://reply.papertrans.cn/1/28/2800/2800-32.png
http://reply.papertrans.cn/1/28/2800/2800-33.png
http://reply.papertrans.cn/1/28/2800/2800-34.png
Submitted on: 23 June 2019.
Revised on: 19 August 2019.
Accepted on: 22 September 2019.
___________________Asian Journal of Mathematics---INT PRESS BOSTON, INC
Submitted on: 26 June 1999.
Revised on: 06 September 1999.
Accepted on: 30 October 1999.
___________________Asian Journal of Mathematics---INT PRESS BOSTON, INC