Either-Or Topology is T4
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Theorem
Let $T = \struct {S, \tau}$ be the either-or space.
Then $T$ is a $T_4$ space.
Proof
Follows from:
$\blacksquare$
Sources
- 1978: Lynn Arthur Steen and J. Arthur Seebach, Jr.: Counterexamples in Topology (2nd ed.) ... (previous) ... (next): Part $\text {II}$: Counterexamples: $17$. Either-Or Topology: $1$