# Definition:Logical Sign (Mathematical Theory)

## Definition

A logical sign of a mathematical theory is a symbol which is specifically pre-defined for the class of the theory.

## Bourbaki Definition

The mathematical theory as defined in Bourbaki's Theory of Sets specifies the logical signs as follows:

The logical signs of a mathematical theory $\mathcal T$ are:

$\Box, \tau, \vee, \rceil$.