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Math Help - fundamental group, free group

  1. #1
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    fundamental group, free group

    Let Y be the complement of the following subset of the plane \mathbb{R}^2:
    \{(x,0) \in \mathbb{R}^2: x \in \mathbb{Z} \}
    Prove that \pi_1(Y) is a free group on a countable set of generators.

    I don't know how to start this problem. Thanks in advance.
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  2. #2
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    Quote Originally Posted by mingcai6172 View Post
    Let Y be the complement of the following subset of the plane \mathbb{R}^2:
    \{(x,0) \in R^2: x \in \mathbb{Z} \}
    Prove that \pi_1(Y) is a free group on a countable set of generators.

    I don't know how to start this problem. Thanks in advance.
    The deformation retract to the wedge product of circles would be the proper way to approach this problem.
    Once you get the deformation retract, I think it would not be hard to prove this.
    Last edited by aliceinwonderland; March 24th 2009 at 02:08 PM. Reason: Error Correction !!
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