The intersection of two straight lines, not only in the acrobatics of formulae but also as far as perspective in concerned, lies at infinity. If we stood on rails and looked along them, optical illusion and lack of experience would help overcome the mathematics. But what if, right at our feet, there were countless intersections of countless rails, and what if they looked anything but straight, and the whole tangle began to revolve? We wouldn’t trust our senses, wouldn’t know which way to turn, and that would be the end of all our infinity. No train would ever get through unscathed.