来自《耶鲁大学开放课程：金融理论 第5集 第5集》

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  So I'm not going to call them goods X and Y anymore.
  这里不再命名为X和Y
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  I'm going to subscript them by time.
  我要用时间来区分它们
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  These are both X because it's the same good,
  它们是同一样东西 都用X表示
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  but they're different goods because they occur at different
  但它们因时间的不同
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  time periods.
  产生差异
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  So Fisher said we can incorporate time simply by
  费雪认为可以用时间
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  having different goods.
  来区分不同的事物
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  So of course people, he said, are going to have some
  当然 今天购买苹果还是明天购买
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  utility of consuming today versus consuming tomorrow,
  给我们带来的效用是不同的
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  and let's say this utility is 1 half log
  我们假设对人A总效用为
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  So I'm going to come back to this in half an hour and explain
  我们一会儿回来讲
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  why Fisher thought that this half made sense.
  为什么这里要存在系数1/2