How Do I Define an Equivalence Relation on a Subset?

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    Equivalence Relation
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Discussion Overview

The discussion revolves around defining an equivalence relation on a subset of the real numbers, specifically within the context of set theory. Participants explore the properties that an equivalence relation must satisfy and seek clarity on how to explicitly define such a relation.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes the necessity of an equivalence relation to satisfy transitive, symmetric, and reflexive properties.
  • Another participant explains that an equivalence relation R from set A to set B is a subset of the Cartesian product A X B, containing ordered pairs (a,b) that are related by R.
  • There is a repeated emphasis on the Cartesian product and its relevance to defining equivalence relations.
  • A participant expresses confusion about how to define an explicit equivalence relation, despite understanding the properties involved.
  • Some participants suggest that the Cartesian product I x I has the required properties for an equivalence relation, but there is uncertainty about its application.
  • Another participant points out that the equivalence relation must be a subset of I x I, indicating a need for clarification on the nature of the relation itself.

Areas of Agreement / Disagreement

Participants do not reach a consensus on how to explicitly define an equivalence relation. There are multiple viewpoints regarding the interpretation and application of the Cartesian product in this context, leading to ongoing confusion and debate.

Contextual Notes

There are limitations in the discussion regarding the explicit definitions of equivalence relations, as well as the assumptions made about the properties of the Cartesian product and its relation to equivalence relations.

mcfc
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If I have a subset, how do I define an equivalence relation.
I understand it has to satisfy three properties:transitive, symmetric and reflexive, but I'm not sure how to give an explicit definition of the equivalence relation, for example on I where
I=\{(x,y) : 0 \le x\le 1 \ \& \ 0 \le y \le 1\}
 
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Do you know what a cartesian product is? If you don't its a very important topic for anyone learning set theory to know.

If you do, then an equivalence relation R from A to B is a subset of A X B. In other words an equivalence relation R contains those ordered pairs (a,b) \in A X B such that a is related to b by R.

In your example that equivalence relation is a subset of \Re X \Re consisting of those (x,y) \in \Re X \Re such that 0 \leq x \leq 1, 0 \leq y \leq 1.

Hope that makes sense to you.
 


CharmedQuark said:
Do you know what a cartesian product is? If you don't its a very important topic for anyone learning set theory to know.

If you do, then an equivalence relation R from A to B is a subset of A X B. In other words an equivalence relation R contains those ordered pairs (a,b) \in A X B such that a is related to b by R.

In your example that equivalence relation is a subset of \Re X \Re consisting of those (x,y) \in \Re X \Re such that 0 \leq x \leq 1, 0 \leq y \leq 1.

Hope that makes sense to you.

HI

That does makes sense, but I can't see how to define an explicit equivalence relation...?
 


mcfc said:
...for example on I where
I=\{(x,y) : 0 \le x\le 1 \ \& \ 0 \le y \le 1\}

I x I has the required properties, right?
 


bpet said:
I x I has the required properties, right?

sorry...I don't follow(again)
 


mcfc said:
sorry...I don't follow(again)

The equivalence relation you gave is a relation on the set I. I X I is the cartesian product of I with itself. Since the relation R is from I to I it is a subset of I X I. An equivalence relation is a set and can be written as such.

Perhaps if you rephrased your question I could be of more help?
 

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