What is the Definition of a Relation in Mathematics?

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Discussion Overview

The discussion centers around the definition of a relation in mathematics, exploring different interpretations and representations of the concept. Participants examine definitions from various mathematical texts and express their preferences, focusing on the theoretical aspects of relations.

Discussion Character

  • Debate/contested

Main Points Raised

  • Some participants note that there is no consensus on the definition of a relation, with some texts defining it as a set of ordered pairs and others as a subset of a Cartesian product.
  • One participant argues that the two definitions are equivalent, suggesting they convey the same underlying concept.
  • Another participant disagrees, stating that the definition involving ordered pairs assumes the ability to construct a set from those pairs, while the Cartesian product definition starts with an existing set and selects a subset.
  • A further contribution presents a formal definition of a relation, stating that a relation R consists of ordered pairs, emphasizing the condition that elements of R must be in the form of ordered pairs.

Areas of Agreement / Disagreement

Participants express differing views on the definitions of a relation, indicating a lack of consensus on the matter. Multiple competing interpretations remain unresolved.

Contextual Notes

Limitations include the potential ambiguity in the definitions and the assumptions underlying each perspective, which may depend on the context in which relations are discussed.

quantum123
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It is kinda strange. There is no agreement on the definition of a relation.
Some books says it is a set of ordered pairs.
Other books says it is a subset of a cartesian product.
How nice if everything can be agreed down to a few axioms like Euclid's elements.

What is your favourite definition of a relation?
 
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The two definitions say the same thing.
 
I do not agree with that. In the definition using ordered pairs, it is assumed that a set can be built from ordered pairs. But in the cartesian definition, a set is provided already, you just use a part of it via subset.
 
I go with:

R \mbox{ is a relation} \Leftrightarrow \forall r(r \in R \Rightarrow \exists x \exists y (r=<x,y>))

This definition states that the elements of R are ordered pairs if and only if R is a relation.
 
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