  The inexpressive Description Logic (DL) $\mathcal{FL}_0$, which has
conjunction and value restriction as its only concept constructors, had fallen
into disrepute when it turned out that reasoning in $\mathcal{FL}_0$ w.r.t.
general TBoxes is ExpTime-complete, i.e., as hard as in the considerably more
expressive logic $\mathcal{ALC}$. In this paper, we rehabilitate
$\mathcal{FL}_0$ by presenting a dedicated subsumption algorithm for
$\mathcal{FL}_0$, which is much simpler than the tableau-based algorithms
employed by highly optimized DL reasoners. Our experiments show that the
performance of our novel algorithm, as prototypically implemented in our
$\mathcal{FL}_o$wer reasoner, compares very well with that of the highly
optimized reasoners. $\mathcal{FL}_o$wer can also deal with ontologies written
in the extension $\mathcal{FL}_{\bot}$ of $\mathcal{FL}_0$ with the top and the
bottom concept by employing a polynomial-time reduction, shown in this paper,
which eliminates top and bottom. We also investigate the complexity of
reasoning in DLs related to the Horn-fragments of $\mathcal{FL}_0$ and
$\mathcal{FL}_{\bot}$.
