Definition:Rational Number Space

Definition
Let $\Q$ be the set of rational numbers.

Let $d: \Q \times \Q \to \R$ be the Euclidean metric on $\Q$.

Let $\tau_d$ be the topology on $\Q$ induced by $d$.

Then $\struct {\Q, \tau_d}$ is the rational number space.

Also see

 * Rational Number Space is Topological Space