Breaking Value Symmetry
  Symmetry is an important factor in solving many constraint satisfaction
problems. One common type of symmetry is when we have symmetric values. In a
recent series of papers, we have studied methods to break value symmetries. Our
results identify computational limits on eliminating value symmetry. For
instance, we prove that pruning all symmetric values is NP-hard in general.
Nevertheless, experiments show that much value symmetry can be broken in
practice. These results may be useful to researchers in planning, scheduling
and other areas as value symmetry occurs in many different domains.
