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Homework Help: About the relation of set

  1. Oct 17, 2009 #1
    1. The problem statement, all variables and given/known data

    Let R denote the following relation in the set N of natural numbers:
    R = {(x, y) | x = 2y}.
    Let E be the “smallest” equivalence relation containing R. Give a complete description of the equivalence classes of E.

    How can I describe it containing infinite set?

    2. Relevant equations

    [An example of smallest equivalence relation can be given as follows::
    Let S = {a, b, c, d} and R = {(a, b), (b, c)}, the smallest equivalence relation containing R is {(a, a), (b, b), (c, c), (d, d), (a, b), (b, a), (a, c), (b, c), (c, a), (c, b)}. ]

    3. The attempt at a solution
  2. jcsd
  3. Oct 20, 2009 #2


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    Science Advisor
    Homework Helper
    Gold Member

    Well, you know you need all pairs (a,a) for reflexivity and all pairs (2a,b) and (a,2b) for symmetry. So the question becomes if you do have all those, is that enough to get transitivity or do you need more?
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