  In a previous paper we lifted Charles Rezk's complete Segal model structure
on the category of simplicial spaces to a Quillen equivalent one on the
category of "relative categories," and our aim in this successor paper is to
obtain a more explicit description of the weak equivalences in this model
structure by showing that these weak equivalences are exactly the
DK-equivalences, i.e. those maps between relative categories which induce a
weak equivalence between their simplicial localizations.
