Give a geometric description of each set in words. Consider the elements of the sets to be coordinates. For example, $\mathbf{R} \times \mathbf{Z}$ is the set $\{(x, n) \mid x \in \mathbf{R}$ and $n \in \mathbf{Z}\} .$ Interpreting the ordered pairs $(x, n)$ as coordinates in the plane, the graph of allsuch ordered pairs is the set of all parallel horizontal lines spaced one unit apart, one of which passes through (0,0).
$$
\mathbf{R} \times \mathbf{R}
$$