来自《耶鲁大学开放课程：博弈论 第9集 第9集》

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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
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  we could think of the strategy (?, ?, 0).
  我可以采用(?, ?, 0)的策略
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  In this strategy I assign, I play rock half the time,
  即我有一半的概率出石头
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  I play paper half the time, but I never play scissors.
  一半的概率出布 但是我就不出剪刀
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  So everyone understand that?
  大家听明白了吗
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  And while we're here let's look at the other extreme.
  接下来我们来看另一种极端情况
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  The probability assigned by my mixed strategy
  混合策略可以赋予一个纯策略