Fort space
From Wikipedia, the free encyclopedia
A Fort space is an example in the theory of topological spaces.
Let X be an infinite set of points, of which P is one. Then a Fort space is defined by X together with all subsets A such that:
- A excludes P, or
- A contains all but a finite number of the points of X
Modified Fort space is similar but has two particular points P and Q. So a subset is declared "open" if:
- A excludes P and Q, or
- A contains all but a finite number of the points of X
[edit] References
- M. K. Fort, Jr. "Nested neighborhoods in Hausdorff spaces." American Mathematical Monthly vol.62 (1955) 372.
- Lynn Arthur Steen and J. Arthur Seebach, Jr., Counterexamples in Topology. Springer-Verlag, New York, 1978. Reprinted by Dover Publications, New York, 1995. ISBN 048668735X (Dover edition).
