Suppose you have some wolves and some dogs. Dogs are named and wolves are not. If you call a dog it will run to you. A wolf would not. So, if you take care of a dog, then (in our pretend situation) you can let it run free. A wolf has to be caged all the time. Any pair of animals can fight, so you need to separate them. On a plane with one line you can place two dogs (one dog in each of the regions): they will not fight as they will be separated by a line, and they will run free. How many dogs and how many wolves can you place on a plane with three lines in general position?