  We use recently introduced Rasmussen invariant to find knots that are
topologically locally-flatly slice but not smoothly slice. We note that this
invariant can be used to give a combinatorial proof of the slice-Bennequin
inequality. Finally, we compute the Rasmussen invariant for quasipositive knots
and show that most of our examples of non-slice knots are not quasipositive
and, to the best of our knowledge, were previously unknown.
