Edward Jack Powley Susan Stepney Automorphisms of Transition Graphs for Elementary Cellular Automata. 125-136 2009 4 J. Cell. Autom. 2 http://www.oldcitypublishing.com/journals/jca-home/jca-issue-contents/jca-volume-4-number-2-2009/jca-4-2-p-125-136/ db/journals/jca/jca4.html#PowleyS09