Relation (set theory)
Concept history
A revision trail for this concept page.
Revision 321
7/8/2026, 7:28:14 AM · Ancient Tree
Concept edited
Compare with revision 320No text changes
1
In [[Set theory|set theory]], a relation $R$ between two sets $A$ and $B$ is a [[Subset|subset]] of the [[Cartesian product|cartesian product]] $A\times B$.2
For $a\in A$ and $b\in B$, one says that $a$ is related to $b$, denoted as $a \;R \;b$, when $(a,b)\in R$.3
4
##### Remarks and examples5
- When $A=B$, one speaks of a relation on $A$.6
- A [[function|function]] is itself a special kind of relation.Revision 320
7/7/2026, 6:37:04 PM · Ancient Tree
Concept edited
Compare with revision 1587 changed lines
1
In set theory, a relation is...1
In [[Set theory|set theory]], a relation $R$ between two sets $A$ and $B$ is a [[Subset|subset]] of the [[Cartesian product|cartesian product]] $A\times B$.2
For $a\in A$ and $b\in B$, one says that $a$ is related to $b$, denoted as $a \;R \;b$, when $(a,b)\in R$.3
4
##### Remarks and examples5
- When $A=B$, one speaks of a relation on $A$.6
- A [[function|function]] is itself a special kind of relation.Revision 158
7/1/2026, 10:20:31 AM · Ancient Tree
Concept created
In set theory, a relation is...