Christopher L. Barrett Harry B. Hunt III Madhav V. Marathe S. S. Ravi Daniel J. Rosenkrantz Richard Edwin Stearns Mayur Thakur Predecessor existence problems for finite discrete dynamical systems. 3-37 2007 386 Theor. Comput. Sci. 1-2 http://dx.doi.org/10.1016/j.tcs.2007.04.026 db/journals/tcs/tcs386.html#BarrettHMRRST07