来自《耶鲁大学开放课程：博弈论 第9集 第9集》

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  in rock, paper, scissors
  我采用(1/3, 1/3, 1/3)的混合策略
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  then Pi is (1/3, 1/3, 1/3)
  那么Pi就是(1/3, 1/3, 1/3)
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  and Pi of rock, so Pi(R)--is a 1/3.
  选择石头的概率即Pi(R)=1/3
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  So without belaboring it,
  我们就再不赘述了
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  that's all I'm doing here, is developing some notation.
  这就是我们要学会的符号表达法
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  Let's immediately encounter two things you might have questions about.
  下面来讲一下你们可能有疑问的地方
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  So the first is, that in principle Pi(Si) could be zero.
  首先是理论上说Pi(Si)可以等于0
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  Just because I'm playing a mixed strategy,
  诚然我采用的是混合策略
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  it doesn't mean I have to involve all of my strategies.
  但并不意味着必须要包含所有的纯策略
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  I could be playing a mixed strategy on two of my strategies
  我的混合策略可能包含两种纯策略
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  and leave the other one with zero probability.
  而赋予另一种纯策略以0概率
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  So, for example, again in rock, paper, scissors,
  还举“石头剪刀布”的例子吧