(a) Prove that if $\mathbf{v}_1, \ldots, \mathbf{v}_m$ are linearly independent, then every subset, e.g., $\mathbf{v}_1, \ldots, \mathbf{v}_k$ with $k<m$, is also linearly independent. (b) Does the same hold true for linearly dependent vectors? Prove or give a counterexample.