  We describe a procedure to compute a projection of $w \in \mathbb{R}^n$ into
the intersection of the so-called \emph{zero-norm} ball $k \mathbb{B}_0$ of
radius $k$, i.e., the set of $k$-sparse vectors, with a box centered at a point
of $k \mathbb{B}_0$. The need for such projection arises in the context of
certain trust-region methods for nonsmooth regularized optimization. Although
the set into which we wish to project is nonconvex, we show that a solution may
be found in $O(n \log(n))$ operations. We describe our Julia implementation and
illustrate our procedure in the context of two trust-region methods for
nonsmooth regularized optimization.
