These lines are critical for shippers needing an economical solution to long-haul transportation. Why do train tracks sit on rocks? How do you train to run in track? The way a person can keep their train from jumping the tracks is to make sure the tracks are well maintained. You can see that this is a rather awkward statement and more difficult to understand than the parallel postulate we use today which is sometimes called the Playfair Postulate , named after the dude who thought it up. We learned that there are four ways to prove lines are parallel.