Naive set theory

Okay kiddo, let's talk about a very important concept in math called set theory. You know how you have a set of toys, like your dolls or cars, right? Well, set theory is like that, except instead of toys we are talking about numbers or objects of any kind.

Now, in naive set theory, people are just starting to learn about sets and don't yet know all the fancy math terms. So, we don't worry too much about things like infinite sets or sets that contain other sets.

Here's an example of a set: let's say you have a collection of fruits - an apple, a banana, and an orange. We can make a set out of these fruits by writing it like this: {apple, banana, orange}. This is called an "unordered set" since the fruits are just listed, and not in any particular order.

Now, let's say you have another set of fruits with an apple, a banana, a grapefruit, and a pear. We could represent this set as {apple, banana, grapefruit, pear}. No matter how many fruits we have or how many times we repeat them, we can always create a set out of them.

There are some special symbols we use in set theory. For example, the symbol "∈" means "is an element of." So if we wrote "apple ∈ {apple, banana, orange}," we are saying that the apple is one of the elements in the set {apple, banana, orange}.

There are some other special symbols in set theory, like "∩" which means "intersection" and "∪" which means "union," but that's a bit more advanced.

The important thing to remember about naive set theory is that it's just the beginning of learning about sets. As you grow older and learn more math, you'll learn about other types of sets and the fancy math terms that go along with them. But for now, just remember that a set is a collection of things, and we can write them down using curly braces like { }.