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Basic basic set theory. Please help. Simple answer will suffice.

  1. Feb 20, 2013 #1
    Hello my name is Andy I'm in highschool, and I have a bit of a confusion or lack of information. Ok so I have been reading a book on set theory, and I keep encountering … ,but up more in the use of a set. Like A,B … but again up more to the middle of the sentence. I feel dumb, I googled it nothing, I've been thinking about it for around 2 hours. I cannot sleep it is bugging me so much. Thank you in advanced!
     
  2. jcsd
  3. Feb 20, 2013 #2

    Simon Bridge

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    You mean you keep encountering three dots like this "..." or "##\cdots##"?
    They are called "ellipsis" and stand for the words "and so on", and mean that things continue as implied by what went before.

    So:
    ##A,B,\cdots## means start going A B C etc and keep going in the same pattern ... so ##\{ 1,3,5,\cdots \}## would represent the set of positive odd numbers
    ##\{ 1,3,5,\cdots,27,29 \}## would be all the odd numbers from 1 through to 27 inclusive.
    They are written like that because it would be boring to list every single member.

    In a sentence it indicates, informally, a longish pause - in a quotation, it means that part of the quote that goes there was deleted for clarity.
    At the end of a sentence it indicates that the sentence has been deliberately left unfinished.

    See:
    http://www.mathsisfun.com/sets/sets-introduction.html
    http://en.wikipedia.org/wiki/Ellipsis
     
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