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

Example 2

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

Antiexamples
Antiexample 1

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