diff --git a/properties/P000198.md b/properties/P000198.md index 081c8d723..c52212bb3 100644 --- a/properties/P000198.md +++ b/properties/P000198.md @@ -16,3 +16,8 @@ That is, every closed discrete subspace of $X$ is countable. Equivalently, every uncountable set $S\subseteq X$ has a limit point in $X$. See {{mr:0776620}} or section a-3 of {{doi:10.1016/B978-0-444-50355-8.X5000-4}}. + +---- +#### Meta-properties + +- If $X$ is covered by countably many subspaces, each having the property, then so does $X$. diff --git a/properties/P000227.md b/properties/P000227.md index 418aff8dc..af105e728 100644 --- a/properties/P000227.md +++ b/properties/P000227.md @@ -22,3 +22,4 @@ Compare with these properties, where $D$ denotes a discrete closed set in $X$: #### Meta-properties - This property is preserved in any finer topology. +- If a closed subspace of $X$ satisfies this property, so does $X$. diff --git a/spaces/S000077/properties/P000227.md b/spaces/S000077/properties/P000227.md new file mode 100644 index 000000000..56bc780a4 --- /dev/null +++ b/spaces/S000077/properties/P000227.md @@ -0,0 +1,7 @@ +--- +space: S000077 +property: P000227 +value: true +--- + +$X$ contains {S63} as a closed subspace, and {S63|P227}. diff --git a/spaces/S000079/properties/P000198.md b/spaces/S000079/properties/P000198.md index dde83cd59..c895dd474 100644 --- a/spaces/S000079/properties/P000198.md +++ b/spaces/S000079/properties/P000198.md @@ -4,11 +4,8 @@ property: P000198 value: true --- -$X$ is a countable union of subspaces -$[0,\omega_1]\times\{n\}$ for $n<\omega$ and $[0,\omega_1)\times\{\omega\}$ which are homeomorphic to {S36} -and {S35}, respectively. -Every closed and discrete subset of $X$ has -countable intersection with each of them -({S36|P198} - and {S35|P198}) -and therefore is countable itself. +$X$ is covered by the countably many subspaces +$[0,\omega_1]\times\{n\}$ for $n<\omega$ and $[0,\omega_1)\times\{\omega\}$, +with each of them {P198} +since {S36|P198} +and {S35|P198}. diff --git a/spaces/S000081/properties/P000198.md b/spaces/S000081/properties/P000198.md new file mode 100644 index 000000000..0cfc0d3e9 --- /dev/null +++ b/spaces/S000081/properties/P000198.md @@ -0,0 +1,14 @@ +--- +space: S000081 +property: P000198 +value: true +refs: +- mathse: 3652735 + name: If $X$ is Lindelof and $Y$ is compact, then $X \times Y$ is Lindelof +--- + +$X$ is the union of finitely many subspaces, each with {P198}: +* $[0, \omega_1] \times [-1, 0)$, because it is {P18} as the product of a {P16} space and a {P18} space (see for example {{mathse:3652735}}), and {T562}. +* $[0, \omega_1] \times (0, 1]$ for the same reason. +* $[0, \omega_1) \times \{0\}$, because it is homeomorphic to {S35} and {S35|P198}. +* $\{\left< \omega_1, 0 \right>\}$, because {S162|P198}. diff --git a/spaces/S000101/properties/P000013.md b/spaces/S000101/properties/P000013.md deleted file mode 100644 index ed88b1096..000000000 --- a/spaces/S000101/properties/P000013.md +++ /dev/null @@ -1,11 +0,0 @@ ---- -space: S000101 -property: P000013 -value: false -refs: -- zb: "0386.54001" - name: Counterexamples in Topology ---- - -Asserted in the General Reference Chart for space #103 -in {{doi:10.1007\/978-1-4612-6290-9_6}}. diff --git a/spaces/S000101/properties/P000017.md b/spaces/S000101/properties/P000017.md deleted file mode 100644 index 7b4ba081a..000000000 --- a/spaces/S000101/properties/P000017.md +++ /dev/null @@ -1,11 +0,0 @@ ---- -space: S000101 -property: P000017 -value: false -refs: -- zb: "0386.54001" - name: Counterexamples in Topology ---- - -Asserted in the General Reference Chart for space #103 -in {{doi:10.1007\/978-1-4612-6290-9_6}}. diff --git a/spaces/S000101/properties/P000227.md b/spaces/S000101/properties/P000227.md new file mode 100644 index 000000000..f968f8b8e --- /dev/null +++ b/spaces/S000101/properties/P000227.md @@ -0,0 +1,12 @@ +--- +space: S000101 +property: P000227 +value: true +refs: + - zb: "0684.54001" + name: General Topology (Engelking, 1989) +--- + +See Exercise 3.1.H(a) in {{zb:0684.54001}}. + +See also . diff --git a/spaces/S000107/properties/P000018.md b/spaces/S000107/properties/P000018.md deleted file mode 100644 index c6a1b614b..000000000 --- a/spaces/S000107/properties/P000018.md +++ /dev/null @@ -1,11 +0,0 @@ ---- -space: S000107 -property: P000018 -value: false -refs: -- zb: "0386.54001" - name: Counterexamples in Topology ---- - -Asserted in the General Reference Chart for space #109 in -{{zb:0386.54001}}. diff --git a/spaces/S000107/properties/P000227.md b/spaces/S000107/properties/P000227.md new file mode 100644 index 000000000..118a3aa91 --- /dev/null +++ b/spaces/S000107/properties/P000227.md @@ -0,0 +1,7 @@ +--- +space: S000107 +property: P000227 +value: true +--- + +$\left\{ 0, 1 \right\}^\omega$ is a closed and discrete subset of cardinality $\mathfrak c$. diff --git a/spaces/S000136/properties/P000018.md b/spaces/S000136/properties/P000018.md deleted file mode 100644 index ad5f45721..000000000 --- a/spaces/S000136/properties/P000018.md +++ /dev/null @@ -1,11 +0,0 @@ ---- -space: S000136 -property: P000018 -value: false -refs: -- zb: "0386.54001" - name: Counterexamples in Topology ---- - -Asserted in the General Reference Chart for space #142 in -{{zb:0386.54001}}. diff --git a/spaces/S000136/properties/P000227.md b/spaces/S000136/properties/P000227.md new file mode 100644 index 000000000..e9f618c6d --- /dev/null +++ b/spaces/S000136/properties/P000227.md @@ -0,0 +1,15 @@ +--- +space: S000136 +property: P000227 +value: true +refs: +- zb: "0386.54001" + name: Counterexamples in Topology +--- + +$X$ contains {S137} as a closed subspace, and {S137|P227}. + +Explicitly, $M$ is a closed and discrete subset of cardinality $\mathfrak c$. + +See item #1 for space #142 in {{zb:0386.54001}}. + diff --git a/spaces/S000137/properties/P000227.md b/spaces/S000137/properties/P000227.md new file mode 100644 index 000000000..4e7cc4197 --- /dev/null +++ b/spaces/S000137/properties/P000227.md @@ -0,0 +1,12 @@ +--- +space: S000137 +property: P000227 +value: true +refs: +- zb: "0386.54001" + name: Counterexamples in Topology +--- + +$M$ is a closed and discrete subset of cardinality $\mathfrak c$. + +See item #1 for space #143 in {{zb:0386.54001}}. diff --git a/spaces/S000153/properties/P000198.md b/spaces/S000153/properties/P000198.md new file mode 100644 index 000000000..655df18d7 --- /dev/null +++ b/spaces/S000153/properties/P000198.md @@ -0,0 +1,9 @@ +--- +space: S000153 +property: P000198 +value: true +--- + +$X$ is the union of the subspaces $\{0\} \times (0, 1)$ and $\left[ 1, \omega_1 \right) \times [0, 1)$, +which are homeomorphic to {S25} and {S38}, respectively. +Each has countable extent, as {S25|P198} and {S38|P198}. diff --git a/spaces/S001103/properties/P000227.md b/spaces/S001103/properties/P000227.md new file mode 100644 index 000000000..030747c33 --- /dev/null +++ b/spaces/S001103/properties/P000227.md @@ -0,0 +1,7 @@ +--- +space: S001103 +property: P000227 +value: true +--- + +$X$ contains a closed subspace homeomorphic to {S101}, and {S101|P227}.