| context | $ X $ |
| definiendum | $ \langle X,\Sigma\rangle\in \mathrm{MeasurableSpace}(X) $ |
| postulate | $ \Sigma \in \mathrm{SigmaAlgebra}(X) $ |
Every σ-algebra gives us a measurable space.
We call a set $X$ measurable if there is a sigma-algebra over it.
Wikipedia: Sigma-algebra