Path-Connected Space is Connected/Proof 2

Theorem

Let $T$ be a topological space which is path-connected.


Then $T$ is connected.


Proof

Let $D$ be the discrete space $\set {0, 1}$.

Let $T$ be path-connected.

Let $f: T \to D$ be a continuous surjection.

Let $x, y \in T: \map f x = 0, \map f y = 1$.

Let $I \subset \R$ be the closed real interval $\closedint 0 1$.

Let $g: I \to T$ be a path from $x$ to $y$.

Then by Composite of Continuous Mappings is Continuous it follows that $f \circ g: I \to D$ is a continuous surjection.

This contradicts the connectedness of $I$ as proved in Subset of Real Numbers is Interval iff Connected.


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Hence the result.

$\blacksquare$


Sources

  • 1975: W.A. Sutherland: Introduction to Metric and Topological Spaces ... (previous) ... (next): $6.4$: Comparison of Definitions: Proposition $6.4.1$
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