ELI5: Explain Like I'm 5

Composition of relations

Have you ever heard the saying "two heads are better than one"? Well, the same goes for relationships between things! When two relationships come together, they can create a whole new relationship that is made up of both of them. This is called the composition of relations.

Imagine you have a basket of apples and another basket of oranges. You can create a new basket of fruit by taking one apple from the first basket and matching it with every orange in the second basket. This would create pairs of apples and oranges, and you would have a new basket of fruit made up of these pairs. This is an example of the composition of relations, where the relationship between the first basket of fruit and the second basket of fruit is combined to create a new relationship.

In math, we use symbols to represent relationships. For example, if we have a relationship that says "A is less than B," we represent it with the symbol "<." We can also use symbols to represent composition of relations. Imagine that we have two relationships, R and S, and we want to create a new relationship that is made up of both of them. We represent this new relationship with the symbol R ∘ S (pronounced "R circle S").

To understand how composition of relations works in math, let's use an example. Imagine we have a relationship R that says "x is the mother of y," and we have another relationship S that says "y is the brother of z." If we want to create a new relationship that combines these two relationships, we would use composition of relations. We would match up every x from relationship R with every y from relationship S that are related through the first relationship, and then match up those y's with every z from relationship S that are related through the second relationship. This would create a new relationship that says "x is the mother of the brother of z."

In summary, composition of relations is when two relationships come together to create a new relationship that is made up of both of them. We use symbols to represent these relationships in math, and we can match up elements from one relationship with elements from another relationship to create the new relationship.
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