Background: Example 10.3. An introduction to the theory of groups, J.Rotman, chapter 10. Abelian groups.
$\mathbb{G} = \mathbb{Q}$ has generators $\left\{ x_1, \cdots, x_n, \cdots \right\}$ and relations $\left\{ x_1-2x_2, x_2-3x_3, \cdots, x_{n-1}-nx_n, \cdots \right\}$.
Surely, $\mathbb{Q}^+$ can be generated using a finite number of generators, or... am I mistaken? To be frank I don't understand this example at all.
Question: Please explain the presentation of $\mathbb{Q}^+$.