Symmetries of Symmetry Breaking Constraints
  Symmetry is an important feature of many constraint programs. We show that
any problem symmetry acting on a set of symmetry breaking constraints can be
used to break symmetry. Different symmetries pick out different solutions in
each symmetry class. This simple but powerful idea can be used in a number of
different ways. We describe one application within model restarts, a search
technique designed to reduce the conflict between symmetry breaking and the
branching heuristic. In model restarts, we restart search periodically with a
random symmetry of the symmetry breaking constraints. Experimental results show
that this symmetry breaking technique is effective in practice on some standard
benchmark problems.
