Symmetry breaking during search in constraint programming

We introduce a method for symmetry breaking during search (SBDS) in constraint programming. It has the great advantage of not interfering with heuristic choices. It guarantees to return a unique solution from each set of symmetrically equivalent ones, which is the one found rst by the variable and value ordering heuristics. We prove this claim, describe a general implementation of SBDS in ILOG Solver, and describe applications to low autocorrelation binary sequences and the n-queens problem. We discuss a version of SBDS that can be applied when there are too many symmetries to reason with individually, and give applications in graph colouring and Ramsey theory.