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spaces/S000107/properties/P000229.md

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Since {S107|P86}, it is enough to show that the path-component of $0$
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is {P229}. By {{mathse:5012784}}, this component equals
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$\mathbb{R}^\infty = \{y : y^n = 0\text{ for all but finitely many }n\}$. We argue that $\mathbb{R}^\infty$ is
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contractible, since {P199|P229}.
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$\mathbb{R}^\infty := \{y : y^n = 0\text{ for all but finitely many }n\}$.
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Because {P199|P229}, we may argue that $\mathbb{R}^\infty$ is
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contractible.
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The claim follows once we argue that $F : \mathbb{R}^\infty \times [0, 1] \to \mathbb{R}^\infty$, $(x, t) \mapsto tx$, is continuous.
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By {{mathse:3961052}}, the subspace topology on $\mathbb{R}^\infty$ coincides with the weak topology,
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where a set $U \subset \mathbb{R}^\infty$ is open if and only if $U \cap \mathbb{R}^n$ is open for
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each $\mathbb{R}^n := \{x \in \mathbb{R}^\infty : x^m = 0\text{ if } m > n\}$. By {{mathse:833227}},
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the product of $\mathbb{R}^\infty \times [0, 1]$ also has 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 $n$.
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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 $n$.
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Then because the restrictions of $F$ to each $\mathbb{R}^n \times [0, 1]$ are continuous and valued in $\mathbb{R}^n$, it follows
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that $F$ is continuous.

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