Either–or topology

In mathematics, the either–or topology is a topological structure defined on the closed interval [−1, 1] by declaring a set open if it either does not contain {0} or does contain (−1, 1).

References

• Steen, Lynn Arthur; Seebach, J. Arthur Jr. (1995) [1978], Counterexamples in Topology (Dover reprint of 1978 ed.), Berlin, New York: Springer-Verlag, ISBN 978-0-486-68735-3, MR 507446