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Math Help - Cardinal numbers proof (identities) & Classes/Sets

  1. #1
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    Unhappy Cardinal numbers proof (identities) & Classes/Sets

    Hi, I need to prove the following rules on cardinal numbers:

    Question1) For all cardinal numbers, κ:

    1) κ + 0 = κ,
    2) κ0 = 0,
    3) κ1 = κ.

    Note: = is in terms of equal cardinality.

    This looks obvious, but I just dont know how to write it in a nice formal way.


    My other question is about Classes / Sets

    Question2) For any two disjoint sets A, B, the class
    Σ(A,B) = {W | W is a connection of A with B}
    is a set.

    How can I show this in a nice clean way?

    Help would be nice!

    Thanks!
    Last edited by blob; August 8th 2010 at 12:52 AM.
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