Here’s a scary scenario: You’ve been put in charge of air traffic control at Newark airport near New York. You need to make sure every plane can taxi between the runway and its gate without hitting any other planes. Let’s bring the power of mathematics to bear on your problem. First, create a big, abstract map of your airport. For each runway, taxiway and gate, mark a point. Then, for each airplane, draw a line connecting these points: If a plane has to go from runway 4L down taxiway K to gate C...