# Definition:Logical Sign (Mathematical Theory)

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## 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:

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

## Sources

- 1968: Nicolas Bourbaki:
*Theory of Sets*... (previous) ... (next): Chapter $\text I$: Description of Formal Mathematics: $1$. Terms and Relations: $1$. Signs and Assemblies