Problem 1. Determine whether the sets \( U \) are \( V \) are subspace of \( \mathbb{R}^{4} \) defined by
\[
\begin{array}{l}
U=\left\{(x, y, z, \theta) \in \mathbb{R}^{4}: x-y-z\right\} \text { and } \\
V^{*}=\left\{(x, y, z, v) \in \mathbb{R}^{4}: x=2 z-1 \text { and } y=v\right\} .
\end{array}
\]