Author: Guest Format: MarkdownItexfound a mathoverflow question where people in the answers are talking about $\sigma$-topological groups and sets equipped with a $\sigma$-topology, so decided to create an article on such objects.
<a href="https://ncatlab.org/nlab/revision/sigma-topological+space/1">v1</a>, <a href="https://ncatlab.org/nlab/show/sigma-topological+space">current</a>
found a mathoverflow question where people in the answers are talking about -topological groups and sets equipped with a -topology, so decided to create an article on such objects.