Closed prabau closed 3 weeks ago
Add theorems implying that under the Lindelof hypothesis, $\aleph$-spaces and $\aleph_0$-spaces are equivalent and $\sigma$-spaces and cosmic spaces are equivalent.
This allows to deduce that 15 more spaces are not $\sigma$-spaces. In particular, the Sorgenfrey line is not a $\sigma$-space: https://topology.pi-base.org/spaces/S000043/properties/P000177
Add theorems implying that under the Lindelof hypothesis, $\aleph$-spaces and $\aleph_0$-spaces are equivalent and $\sigma$-spaces and cosmic spaces are equivalent.
This allows to deduce that 15 more spaces are not $\sigma$-spaces. In particular, the Sorgenfrey line is not a $\sigma$-space: https://topology.pi-base.org/spaces/S000043/properties/P000177