Baumert, L. D. and Golomb, S. W. "Backtrack Programming." J. Ass. Comp. Machinery12, 516-524, 1965.Knuth, D. E. "Estimating the Efficiency of Backtrack Programs." Math. Comput.29, 122-136, 1975.Lauwerier, H. A. Fractals: Endlessly Repeated Geometrical Figures. Princeton, NJ: Princeton University Press, 1991.Skiena, S. "Backtracking and Distinct Permutations." §1.1.5 in Implementing Discrete Mathematics: Combinatorics and Graph Theory with Mathematica. Reading, MA: Addison-Wesley, pp. 12-14, 1990.Skiena, S. S. The Algorithm Design Manual. New York: Springer-Verlag, 1997.Wilf, H. "Backtrack: An Expected Time Algorithm for the Graph Coloring Problem." Info. Proc. Let.18, 119-121, 1984.