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In my course notes of topology, we have seen the following example of a space that is connected but not path-connected.

Define $X := \{(0,0)\} \cup \{(x,\sin(\frac{1}{x}))\mid x > 0\}$

I understand why this is connected but I have troubles by arguing why it's not path-connected. my opinion: consider $X$ is path-connected

  • for $x = (0,0)$ and $y = (1,\sin(1))$ , there is a continuous function $f\colon [0,1] \rightarrow X: 0 \mapsto x, 1 \mapsto y$

  • because $[0,1]$ is compact and $f$ is continuous, $X$ is compact. I think that $X$ is not compact but I can't prove why. If I can prove this, $f$ can't be continuous and then it's ok.

Dan Rust
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Koen
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    It's not $X$ that is compact, but the trace of the path, $f([0,,1])$. If the path existed, that would contain $Y = {(0,0)} \cup {(x,\sin (1/x)) : 0 < x \leqslant 1}$, which then would also be compact. – Daniel Fischer Aug 07 '13 at 09:30

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