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Notation question

  1. Nov 12, 2007 #1
    I have something like this:


    What am I looking at? Is this [tex]x_{1}\cup x_{2}\cup x_{3}\cup ...\cup x_{N}[/tex]?
    Last edited: Nov 12, 2007
  2. jcsd
  3. Nov 12, 2007 #2

    Ben Niehoff

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    Yes, it's a union over some collection of sets.
  4. Nov 12, 2007 #3


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    Not necessarily because N can be infinite say...

    x1 U x2 U x3 U ...

    But also, N can be uncountable, which means listing them in whatever way is pointless and incorrect.
  5. Nov 12, 2007 #4
    Thanks, Folland started using it without prior explanation (that I noticed).

    It's the only interpretation that I could think of that made sense, but I didn't want to guess since it's already part of one theorem and one definition and if I guessed wrong then everything I did using those could be thrown off.
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