Either–or topology

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

[edit] References

• Steen, Lynn Arthur; Seebach, J. Arthur Jr. (1995) [1978], Counterexamples in Topology (Dover reprint of 1978 ed.), Berlin, New York: Springer-Verlag, MR507446, ISBN 978-0-486-68735-3