ABSTRACT
Imagine that you’re in a wilderness area, equipped with a compass and a weak pair of binoculars. You start out at tree X, walk to rock Y, and then move to tree Z (Figure 1). You’re now too far away to see tree X with the binoculars. You walk to a new position S and from there, you should be able to see tree X again. You look in the binoculars, and tree X isn’t where it’s supposed to be. In fact, rock Y seems to have moved to where X had been.
