  We extend previous proofs that violations of the null energy condition (NEC)
are a generic and universal feature of traversable wormholes to completely
non-symmetric time-dependent wormholes. We show that the analysis can be
phrased purely in terms of local geometry at and near the wormhole throat, and
do not have to make any technical assumptions about asymptotic flatness or
other global properties. A key aspect of the analysis is the demonstration that
time-dependent wormholes have two throats, one for each direction through the
wormhole, and that the two throats coalesce only for the case of a static
wormhole.
