Category:Definitions/Fort Spaces

This category contains definitions related to Fort Spaces.
Related results can be found in Category:Fort Spaces.

Let $S$ be an infinite set.

Let $p \in S$ be a particular point of $S$.

Let $\tau_p \subseteq \powerset S$ be a subset of the power set of $S$ defined as:

$\tau_p = \leftset {U \subseteq S: p \in \relcomp S U} \text { or } \set {U \subseteq S: \relcomp S U}$ is finite$\rightset{}$

That is, $\tau_p$ is the set of all subsets of $S$ whose complement in $S$ either contains $p$ or is finite.

Then $\tau_p$ is a Fort topology on $S$, and the topological space $T = \struct {S, \tau_p}$ is a Fort space.