When different parts of a surface collide, a topological change must
be made.
For simplicity, we make the assumption that if 
is a
normal to 
, then so is 
. The collision is thus between
oppositely oriented segments (since segments bound solids and/or
``outside'' regions); as a limiting case, two corners may collide, in
which case either pair of oppositely oriented normals could be used.
If one facet completely overlaps the opposite, the shorter facet is
completely removed, as is the section of the longer facet that
overlaps the shorter. Then the remaining portions of the longer facet
are connected to the neighbors of the shorter one. If the opposing
facets only partially overlap, then the portion of overlap is removed
from both facets, and the remaining piece is attached to the
loose former neighbor of the other facet.
This cutting and pasting will produce bad corners, i.e. ones which
omit normals of the Wulff shape (unless is a parallelogram).
These illegal corners will have infinite chemical potential and are
places where zero-length 
facets must be inserted until
none of the normals of between neighboring edges are omitted.
These new edges will move with initially infinite velocity, although
the velocity will immediately become finite as the edges become of
non-zero length. it remains to be shown that there is indeed an unique
evolution in SD or in SALK out of such a corner.
In SALK it is possible for an entire connected component to shrink to
a point if there is more than one component surrounded by the same
transport medium. If this occurs, all its edges are simultaneously
removed. The total average curvature, which is the chemical potential
in the transport medium, drops by an amount equal to the length of the
boundary of (or some weighted sum of the 
if the 
are not all equal to 1).