1. Finding topology in a factory: configuration spaces;Abrams;Am. Math. Mon.,2002
2. The Knot Book: An Elementary Introduction to the Mathematical Theory of Knots;Adams,1994
3. Introduction to Topology: Pure and Applied;Adams,2008
4. Hex games and twist maps on the annulus;Alpern;Am. Math. Mon.,1991
5. The solution of the four-color-map problem;Appel;Sci. Am.,1977