Double Pointed Fortissimo Space is Not Sigma-Compact
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Theorem
Let $T = \left({S, \tau}\right)$ be a Fortissimo space.
Let $T \times D$ be the double pointed topology on $T$.
Then $T \times D$ is not $\sigma$-compact.
Proof
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Sources
- Lynn Arthur Steen and J. Arthur Seebach, Jr.: Counterexamples in Topology (1970)... (previous)... (next): $\text{II}: \ 25: \ 4$
