This is the author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Applied Probability Trust, The University, School Mathematics Statistics and can be found at: http://www.appliedprobability.org/content.aspx?Group=journals&Page=apjournals.
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机译：这是作者所接受的经同行评审的最终手稿。该发表的文章的版权归美国大学数学统计局应用概率基金会（Applied Probability Trust）所有，可以在以下网站找到：http://www.appliedprobability.org/content.aspx?Group=journals&Page=apjournals。
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