##
*
Description of Sets
*

A *set* is a collection of things.

We call the "things" ... the *elements* of the set.

Two sets are *equal* if they have the same elements.

2 ---------- begin topic:

We use curly braces to denote sets: {3} is a set of one element, which is the number three.

3 ---------- begin topic:

The symbol means *"is an element of"*, while

the symbol means *"is not an element of"***.**

Thus we write

3{3} and 4{3}.

4 ---------- begin topic:

Capital letters are frequently used to stand for sets,

and small letters are frequently used to stand for the elements of a set.

Thus we write *x**A* **.**

5 ---------- begin topic:

Particular sets are often indicated using the following notation**:**

*A* = { *x* : statement about *x* },

which is read as follows**:**

*A* is the set of all elements, *x*, such that the statement about *x* is true.