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7 changes: 5 additions & 2 deletions spaces/S000205/README.md
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Expand Up @@ -6,12 +6,15 @@ refs:
name: Warsaw circle on Wikipedia
- doi: 10.1016/j.topol.2013.07.001
name: Milnor–Thurston homology groups of the Warsaw Circle (J. Przewocki)
- mathse: 2423154
name: First Betti number of a Reeb graph is not greater than that of the space?
---

The set $X=\{(x, \sin\frac{1}{x}):x \in (0,1]\} \cup \{(0,y):y \in [-2,1]\} \cup \{(x,-2):x\in[0,1]\} \cup \{(1,y):y \in [-2,\sin 1]\}$ with the subspace topology inherited from $\mathbb{R}^2$.

It consists of {S114} together with an extra arc joining its rightmost point to the point $(0,-1)$.
See {{wikipedia:Warsaw_circle}} or section 3 of {{doi:10.1016/j.topol.2013.07.001}}
See {{wikipedia:Warsaw_circle}} or section 3 of {{doi:10.1016/j.topol.2013.07.001}}.

Note: There are a few closely related but non-isomorphic variants of the *Warsaw circle*.
Note: There are a few closely related but non-isomorphic variants of the *Warsaw circle*
(see the pictures in {{mathse:2423154}} for two of them).
The description chosen here seems to be the most common.
10 changes: 10 additions & 0 deletions spaces/S000205/properties/P000089.md
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---
space: S000205
property: P000089
value: true
refs:
- mathse: 4775855
name: Warsaw circle has the fixed point property
---

See answer to {{mathse:4775855}}.
8 changes: 8 additions & 0 deletions spaces/S000205/properties/P000204.md
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---
space: S000205
property: P000204
value: false
---

Let $p \in X$. If $p \notin \{0\}\times [-1,1]$, then $X\setminus \{p\}$ is homotopy equivalent to {S114} and {S114|P36}.
Otherwise $Y = X \setminus (\{0\}\times [-1,1])$ is dense in $X \setminus \{p\}$. Hence $X \setminus \{p\}$ is connected as $Y$ is clearly (path-)connected.