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Math Help - basic group theory Q

  1. #1
    Senior Member sfspitfire23's Avatar
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    basic group theory Q

    Guys, I took abstract algebra a few years back and I'm trying to refresh my memory. Heres a Q:


    True or False: If (G, ∗) is a group that has two or more elements , then the binary operation ∗ is a bijection from G G to G.

    I think sometimes true. Wouldn't the identity*identity=identity? But then I'm sure there are other examples of non identity elements when multiplied equaling the same number and thus not a bijection.

    Anyone think of examples?
    Last edited by CaptainBlack; October 9th 2011 at 10:32 AM.
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  2. #2
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    Re: basic Q

    GxG has how many elements?
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  3. #3
    Senior Member sfspitfire23's Avatar
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    Re: basic Q

    I think greater than two...been awhile, does this make sense?
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  4. #4
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    Re: basic Q

    GxG has |G|^2 elements (so 4 if |G| = 2, 9 if |G| = 3, etc...)

    how can there possibly be a bijection between GxG and G?
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  5. #5
    Senior Member sfspitfire23's Avatar
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    Re: basic Q

    but what if G is not finite (i.e. both G x G and G have an infinite number of elements), then we can't use that argument?
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  6. #6
    Grand Panjandrum
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    Re: basic Q

    Quote Originally Posted by Deveno View Post
    GxG has how many elements?
    Please quote the question and preferably whatever post you are replying to, that way we do not need to worry so much about the original questions being deleted, and it is easier to follow what your post is about.

    CB
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