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Confused about set-theoretic definition of a function

  1. Sep 15, 2011 #1
    I have read that a function f: A -> B can be defined as an ordered triple of sets (A,B,X), where X is the set of all ordered pairs [itex] X = \{(a,f(a)) \in A \times B\}. [/itex] But ordered tuples are really functions from [itex]\{1, ..., n\}[/itex] to (whatever set under consideration), right? So isn't this a circular definition? Or is there a more basic definition of functions that does not involve tuples? Any help would be greatly appreciated.
  2. jcsd
  3. Sep 15, 2011 #2
    No, this is not true. The ordered tuple (a,b) is defined as {{a},{a,b}}. It's not defined as a function.
  4. Sep 15, 2011 #3
    But aren't tuples other than the ordered pair defined as functions, so that the definition of functions as triples would still be circular?
  5. Sep 15, 2011 #4
    No, triples can be defined as


    And the definition of a function only uses ordered pairs and triples. So there is nothing circular.
  6. Sep 15, 2011 #5
    Oh I think I get it now. Thanks micromass!
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