diff --git a/spaces/S000107/properties/P000229.md b/spaces/S000107/properties/P000229.md new file mode 100644 index 0000000000..ca8b0bc5ea --- /dev/null +++ b/spaces/S000107/properties/P000229.md @@ -0,0 +1,23 @@ +--- +space: S000107 +property: P000229 +value: true +refs: +- mathse: 3961052 + name: Answer to "Is the weak topology on $\mathbb{R}^{\infty}$ the same as the box topology?" +- mathse: 833227 + name: Answer to "(Certain) colimit and product in category of topological spaces" +--- + +Since {S107|P86}, it is enough to show that the path-component of $0$ +is {P229}. By {{mathse:5012784}}, this component equals +$\mathbb{R}^\infty := \{y : y^n = 0\text{ for all but finitely many }n\}$. +Then it is enough to argue that $\mathbb{R}^\infty$ is contractible ([Explore](https://topology.pi-base.org/spaces?q=contractible+%2B+%7ESemilocally+simply+connected)). +This follows once we argue that $F : \mathbb{R}^\infty \times [0, 1] \to \mathbb{R}^\infty$, $(x, t) \mapsto tx$, is continuous. + +By {{mathse:3961052}}, the subspace topology on $\mathbb{R}^\infty$ coincides with the weak topology, +where a set $U \subset \mathbb{R}^\infty$ is open if and only if $U \cap \mathbb{R}^n$ is open for +each $\mathbb{R}^n := \{x \in \mathbb{R}^\infty : x^m = 0\text{ if } m > n\}$. By {{mathse:833227}}, +the product topology on $\mathbb{R}^\infty \times [0, 1]$ also coincides with the weak topology, where again a set $U \subset \mathbb{R}^\infty \times [0, 1]$ is open if and only if $U \cap (\mathbb{R}^n \times [0, 1])$ is open for each $n$. +Then because the restrictions of $F$ to each $\mathbb{R}^n \times [0, 1]$ are continuous, it follows +that $F$ is continuous. diff --git a/spaces/S000107/properties/P000041.md b/spaces/S000107/properties/P000234.md similarity index 85% rename from spaces/S000107/properties/P000041.md rename to spaces/S000107/properties/P000234.md index ab470ec1d0..4627b12ef5 100644 --- a/spaces/S000107/properties/P000041.md +++ b/spaces/S000107/properties/P000234.md @@ -1,10 +1,10 @@ --- space: S000107 -property: P000041 +property: P000234 value: false refs: - mathse: 5012784 name: Answer to "Is $\ell^\infty$ with box topology connected?" --- -By {{mathse:5012784}} the connected component of an arbitrary point $x\in X$ is $A = \{y : y_n = x_n\text{ for all but finitely many }n\}$. Since $\text{int}(A) = \emptyset$, it follows that $x$ has no connected neighbourhoods. +By {{mathse:5012784}} the connected component of an arbitrary point $x\in X$ is $A = \{y : y_n = x_n\text{ for all but finitely many }n\}$. Since $\text{int}(A) = \emptyset$, it follows that $A$ is not open.