Arens–Fort space

In mathematics, the Arens–Fort space is a special example in the theory of topological spaces, named for Richard Friederich Arens and M. K. Fort, Jr.

The Arens–Fort space is the topological space

, τ )

is the set of ordered pairs of non-negative integers

is open, that is, belongs to

τ ,

if and only if: In other words, an open set is only "allowed" to contain

if only a finite number of its columns contain significant gaps, where a gap in a column is significant if it omits an infinite number of points.

is a cluster point of