Hatching is when you add lines to drawings to make light and dark areas. And when you cross lines over each other, it's called cross-hatching. To give it a try, you will need: a pencil and some paper.

For two decades, the conjecture stumped anyone who tried to prove it. The best progress came in 2003, when Jean Bourgain, a legendarily astute mathematician, inched a tiny bit closer in one special ...