Points are Path-Connected iff Contained in Path-Connected Set

Theorem

Let $T = \struct {S, \tau}$ be a topological space.

Let $x, y \in S$

Then:

$x, y$ are path-connected points in $T$ if and only if there exists a path-connected set of $T$ containing $x$ and $y$.

Proof

Necessary Condition

Let $x, y$ be path-connected points in $T$.

Let $\gamma: \closedint 0 1 \to T$ be a path from $x$ to $y$.

From Image of Path is Path-Connected Set, $\Img \gamma$ is a path-connected set of $T$ containing $x$ and $y$.

The result follows.

$\Box$

Sufficient Condition

Let $B$ be a path-connected set of $T$ containing $x$ and $y$.

Then there exists a path $\gamma: \closedint 0 1 \to B$ from $x$ to $y$.

Let $i_B: B \to S$ be the inclusion mapping from $B$ into $S$.

From Composite of Continuous Mappings is Continuous, $i_B \circ g: \closedint 0 1 \to T$ is continuous.

Hence $i_B \circ g$ is a path from $x$ to $y$ in $T$.

$\blacksquare$