In the 150-year history of responding to the four-color problem the mathematics community has sent off tubers in many directions. These directions have included looking at coloring problems for surfaces other than the plane, coloring objects other than the faces of a map (e.g. knots), and finding applications for these ideas. Good problems are as important as the answers we find for them.

These web essays are designed for those who have already discovered the joys of mathematics as well as for those who may be uncomfortable with mathematics.
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