diff --git a/spaces/S000217/README.md b/spaces/S000217/README.md new file mode 100644 index 000000000..aaedc7335 --- /dev/null +++ b/spaces/S000217/README.md @@ -0,0 +1,14 @@ +--- +uid: S000217 +name: Left ray topology on $\omega_1$ +refs: + - wikipedia: Alexandrov_topology + name: Alexandrov topology on Wikipedia +--- + +Let $X=\omega_1$, with a base for the topology consisting of the left rays +$[0,\alpha]=[0,\alpha+1)$ for $\alpha\in\omega_1$. + +The open sets are the downward closed subsets of $X$, which are $X$, $\emptyset$, +the basic open sets above, and the rays $[0,\alpha)$ with $\alpha$ limit ordinal. +This is the Alexandrov topology for the reverse ordering on $\omega_1$. diff --git a/spaces/S000217/properties/P000001.md b/spaces/S000217/properties/P000001.md new file mode 100644 index 000000000..3efba79c7 --- /dev/null +++ b/spaces/S000217/properties/P000001.md @@ -0,0 +1,7 @@ +--- +space: S000217 +property: P000001 +value: true +--- + +Given $\alpha<\beta$ in $X$, the open set $[0,\alpha]$ contains $\alpha$ and not $\beta$. diff --git a/spaces/S000217/properties/P000093.md b/spaces/S000217/properties/P000093.md new file mode 100644 index 000000000..e23fd78b6 --- /dev/null +++ b/spaces/S000217/properties/P000093.md @@ -0,0 +1,7 @@ +--- +space: S000217 +property: P000093 +value: true +--- + +Each basic open set of the form $[0,\alpha]$ for $\alpha\in\omega_1$ is countable. diff --git a/spaces/S000217/properties/P000114.md b/spaces/S000217/properties/P000114.md new file mode 100644 index 000000000..1ebdc2ca2 --- /dev/null +++ b/spaces/S000217/properties/P000114.md @@ -0,0 +1,7 @@ +--- +space: S000217 +property: P000114 +value: true +--- + +By construction. diff --git a/spaces/S000217/properties/P000196.md b/spaces/S000217/properties/P000196.md new file mode 100644 index 000000000..94c332189 --- /dev/null +++ b/spaces/S000217/properties/P000196.md @@ -0,0 +1,7 @@ +--- +space: S000217 +property: P000196 +value: true +--- + +By construction. diff --git a/spaces/S000217/properties/P000226.md b/spaces/S000217/properties/P000226.md new file mode 100644 index 000000000..5c6b467a9 --- /dev/null +++ b/spaces/S000217/properties/P000226.md @@ -0,0 +1,8 @@ +--- +space: S000217 +property: P000226 +value: true +--- + +Since the ordinal numbers are well-ordered, +every nonempty collection of open sets has a minimal element.