  Given a graph on $n$ vertices and an integer $k$, the feedback vertex set
problem asks for the deletion of at most $k$ vertices to make the graph
acyclic. We show that a greedy branching algorithm, which always branches on an
undecided vertex with the largest degree, runs in single-exponential time,
i.e., $O(c^k\cdot n^2)$ for some constant $c$.
