Confused about set-theoretic definition of a function

In summary, the conversation discusses the definition of a function f: A -> B as an ordered triple of sets (A,B,X), where X is the set of all ordered pairs (a,f(a)) in A x B. There is a question about whether this definition is circular, as tuples are also defined as functions. However, it is clarified that triples can be defined using ordered pairs and the definition of a function does not involve tuples, making it not circular.
  • #1
poochie_d
18
0
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.
 
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  • #2
poochie_d said:
But ordered tuples are really functions from [itex]\{1, ..., n\}[/itex] 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.
 
  • #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?
 
  • #4
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

[tex](a,b,c)=((a,b),c)[/tex]

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

1. What is a function in set theory?

In set theory, a function is a relation between two sets, where each element in the first set (the domain) is paired with exactly one element in the second set (the codomain). This means that for every input, there is only one output.

2. How is a function defined in set theory?

In set theory, a function is defined as a subset of the Cartesian product of the domain and codomain, where each element in the domain is paired with exactly one element in the codomain. This can be represented using ordered pairs, with the first element being the input and the second element being the output.

3. What is the difference between a function and a relation in set theory?

In set theory, a function is a special type of relation where each input is paired with exactly one output. A relation, on the other hand, can pair multiple inputs with multiple outputs. In other words, a function is a subset of a relation that follows a specific rule.

4. How can a function be represented in set notation?

A function can be represented in set notation as a set of ordered pairs, where the first element in each pair is an element from the domain and the second element is an element from the codomain. For example, the function f(x) = 2x could be written as {(1,2), (2,4), (3,6), ...}.

5. What is the importance of functions in mathematics?

Functions are important in mathematics because they provide a way to map inputs to outputs, which is essential in solving many mathematical problems. Functions also allow us to describe and analyze relationships between sets in a precise and structured way.

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