1. (1) R. E. Korf and A. Felner: “Disjoint pattern database heuristics”, Artificial Intelligence, Vol. 134, No. 1, pp. 9-22 (2002)
2. (2) R. E. Korf: “Depth-first iterative-deepening: An optimal admissible tree search”, Artificial Intelligence, Vol. 27, No. 1, pp. 97-109 (1985)
3. (3) P. E. Hart, N. J. Nilsson, and B. Raphael: “A formal basis for the heuristic determination of minimum cost paths”, Systems Science and Cybernetics, IEEE Transactions on, Vol. 4, No. 2, pp. 100-107 (1968)
4. (4) Wikipedia: Admissible heuristic—Wikipedia, The Free Encyclopedia (2017)
5. (5) Wikipedia: Klotsuki—Wikipedia, The Free Encyclopedia (2014)