Confused about set-theoretic definition of a function

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Discussion Overview

The discussion centers around the set-theoretic definition of a function, specifically the characterization of a function as an ordered triple of sets and the implications of using ordered pairs and tuples in this definition. Participants explore whether this definition is circular and seek a more fundamental understanding of functions without relying on tuples.

Discussion Character

  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether defining a function as an ordered triple of sets (A, B, X) is circular, given that ordered tuples can be seen as functions from a set of indices to another set.
  • Another participant asserts that ordered tuples are defined as sets and not as functions, challenging the initial claim of circularity.
  • A further inquiry is made about the nature of tuples and whether their definitions as functions could still imply circularity in defining functions as triples.
  • A response clarifies that triples can be defined in terms of ordered pairs, suggesting that the definition of a function does not rely on circular reasoning.
  • A participant expresses understanding after the clarifications provided by another member.

Areas of Agreement / Disagreement

The discussion reflects disagreement regarding the circularity of the definition of functions. Some participants argue against the circularity, while others raise concerns about the definitions of tuples and their implications.

Contextual Notes

Participants express uncertainty about the foundational definitions of functions and tuples, and the discussion does not resolve whether a more basic definition exists that avoids the use of tuples.

poochie_d
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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 X = \{(a,f(a)) \in A \times B\}. But ordered tuples are really functions from \{1, ..., n\} 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.
 
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poochie_d said:
But ordered tuples are really functions from \{1, ..., n\} to (whatever set under consideration), right?

No, this is not true. The ordered tuple (a,b) is defined as {{a},{a,b}}. It's not defined as a function.
 
But aren't tuples other than the ordered pair defined as functions, so that the definition of functions as triples would still be circular?
 
poochie_d said:
But aren't tuples other than the ordered pair defined as functions, so that the definition of functions as triples would still be circular?

No, triples can be defined as

(a,b,c)=((a,b),c)

And the definition of a function only uses ordered pairs and triples. So there is nothing circular.
 
Oh I think I get it now. Thanks micromass!
 

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