 \le \frac{\lambda}{0} \|v\| + \lambda \|\beta^\star\| - \lambda \|\beta^\star+v\|\,,     \end{aligned}$$ where $v = {\widehat{\beta}}-\beta^\star$. As a consequence, $v\in {{\color{ygcolor}\Xi}}$, where ${{\color{ygcolor}\Xi}}$ is given by . 