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Uncountable sets need help

  1. Dec 30, 2012 #1
    hello im struggled with a qustion
    let B be a countable subset of uncountable set A.
    Prove |A-B|=|A|
    i know how to prove that A-B is uncountable
    but how do i show 1:1 with A?

    thanks ahead guys
     
    Last edited: Dec 30, 2012
  2. jcsd
  3. Dec 30, 2012 #2

    tiny-tim

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    welcome to pf!

    hello ranykar! welcome to pf! :smile:

    (no, you're struggling with the question! :wink:

    or being strangled by it? :yuck:)​


    hint: assume the opposite :wink:

    (ie, that A-B is countable)
     
  4. Dec 30, 2012 #3
    Re: welcome to pf!

    tnx but thats not what i was asking.
    i know that A-B is uncountable.
    but how do i show 1:1 with A??
     
  5. Dec 31, 2012 #4

    Bacle2

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    Try doing a reordering of A , so that B is an initial segment of A.
     
  6. Dec 31, 2012 #5

    tiny-tim

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  7. Dec 31, 2012 #6

    Bacle2

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    I think s/he wants to set up an actual bijection between A and A\B .
     
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