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Open and closed functions

  1. Sep 14, 2005 #1


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    I'm trying to understand open and closed functions, and right now I'm on the projection from R^2 to R, with f(x,y)=x. It seems this is both open and closed, but the wikipedia article on open and closed functions seems to disagree:

    I don't understand what exactly A is, and I can't think of any counterexamples myself. Are they talking about the same function as me? Can someone explain any of this?
  2. jcsd
  3. Sep 14, 2005 #2


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    In their example, A is the hyperbola given by the equation xy = 1.
  4. Sep 14, 2005 #3


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    I see. So it's not closed. Thanks.
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