## Borel algebra

### Set

 context $\langle X,\mathcal T\rangle \in \mathrm{TopSpace}(X)$
 definiendum $\mathcal B(X):\equiv \sigma(\mathcal T)$

### Discussion

The Borel algebra of $X$ is the smallest σ-algebra formed from its open sets.

### Reference

Wikipedia: Borel set