Definition:Path-Connected/Topology/Set

Definition
Let $T = \left({X, \vartheta}\right)$ be a topological space.

Let $U \subseteq X$ be a subset of $T$.

Let $T\,' = \left({U, \vartheta_U}\right)$ be the subspace of $T$ induced by $U$.

Then $U$ is path-connected in $T$ iff every two points in $U$ are path-connected in $T\,'$.

That is, $U$ is path-connected iff:
 * for every $x, y \in U, \exists$ a continuous mapping $f: \left[{0 \,.\,.\, 1}\right] \to U$ such that $f \left({0}\right) = x$ and $f \left({1}\right) = y$.