Rational Number Space is Topological Space/Proof 2

Proof
Let $\left({\R, \tau_d}\right)$ be the real number space $\R$ under the Euclidean topology $\tau_d$.

By definition of rational numbers, $\Q \subseteq \R$.

From Topological Subspace is Topological Space we have that $\left({\Q, \tau_d}\right)$ is a topology.