Vikraman Arvind Richard Beigel Antoni Lozano The Complexity of Modular Graph Automorphism. 1299-1320 2000 30 SIAM J. Comput. 4 http://epubs.siam.org/sam-bin/dbq/article/35822 db/journals/siamcomp/siamcomp30.html#ArvindBL00