  In the early 1980's Mike Freedman showed that all knots with trivial
Alexander polynomial are topologically slice (with fundamental group Z). This
paper contains the first new examples of topologically slice knots. In fact, we
give a sufficient homological condition under which a knot is slice with
fundamental group Z semi-direct product Z[1/2]. These two fundamental groups
are known to be the only solvable ribbon groups. Our homological condition
implies that the Alexander polynomial equals (t-2)(t^{-1}-2) but also contains
information about the metabelian cover of the knot complement (since there are
many non-slice knots with this Alexander polynomial).
  Erratum (attached): In Figure 1.5 we gave an incorrect example for Theorem
1.3. We present a correct example.
