Eugene M. Luks Amitabha Roy The Complexity of Symmetry-Breaking Formulas. 19-45 2004 41 Ann. Math. Artif. Intell. 1 http://www.springerlink.com/index/10.1023/B:AMAI.0000018578.92398.10 db/journals/amai/amai41.html#LuksR04