# Open

Revision as of 20:50, 10 December 2018 by Jflopezfernandez (talk | contribs)

Let $X$ be a topological space with topology $\mathscr{T}$. An open set $U$ is in $\mathscr{T}$. Therefore, a topological space may be defined as a set $X$ together with a collection of subsets of $X$, called *open sets*, such that $\emptyset$ and $X$ are both open, and such that arbitrary unions and finite intersections of open sets are open.^{[1]}

## References

- ↑ Munkres, James R. Topology, 2015. pg. 74.