1. [1] Arkin, E.M., Bender, M.A., Demaine, E.D., Demaine, M.L., Mitchell, J.S.B., Sethia, S. and Skiena, S.S.: When can you fold a map?, Comput. Geom. Theory Appl., Vol.29, No.1, pp.23-46 (2004).
2. [2] Cardinal, J., Demaine, E.D., Demaine, M.L., Imahori, S., Ito, T., Kiyomi, M., Langerman, S., Uehara, R. and Uno, T.: Algorithmic Folding Complexity, Graphs and Combinatorics, Vol.27, pp.341-351, DOI: 10.1007/s00373-011-1019-0 (2011).
3. [3] Garey, M. and Johnson, D.: Computers and Intractability — A Guide to the Theory of NP-Completeness, Freeman (1979).
4. [4] Lehman, F.H.: Puzzle. U.S. Patent 856, 196 (June 1907).
5. [5] Scherphuis, J.: Jaap's Puzzle Page: Transposer/Trixxy/Stained (2009), available from <http://www.jaapsch.net/puzzles/trixxy.htm>.