User:Jshflynn/Definition:Alphabet

Definition
Let $\Sigma$ be a non-empty finite set.

In the context of formal language theory $\Sigma$ is referred to as an alphabet.

Examples
Example 1

The set $\{a, b, c\}$ is an alphabet.

Example 2

The set $\{$begin, end, while, do, if, then$\}$ is an alphabet similar to ones used in programming languages.

Antiexamples
Antiexample 1

The set $\emptyset$ fails to be an alphabet are required to be non-empty.