# Definition:Sign (Mathematical Theory)

## Definition

A sign of a mathematical theory is a symbol which has a specific meaning in the theory, as follows:

1. A logical sign;
2. A letter;
3. A specific sign.

A logical sign is a sign which has a specific meaning and definition in a particular class of mathematical theory.

A letter is a more or less arbitrary symbol whose definition depends on the specific context.

For a given mathematical theory, there are signs which are specific to the use to which the theory is being put. These are the specific signs.