Take an outline map of the lower 48 U.S. states and four crayons. Can you shade in the map so that every state is a different color than each of its neighbors, without resorting to a fifth color? This ...

In the 1970s, a remarkable thing was done; a computer was used to solve a math problem. This, in and of itself, was not remarkable. The difference engine could do it. But this problem was the first ...