That one is actually not very hard. Imagine the world pacman lives in: It's rolled up with a finite width in both of its two dimensions. Pacman can move left-ri

That one is actually not very hard. Imagine the world pacman lives in: It's rolled up with a finite width in both of its two dimensions. Pacman can move left-right and up-down but after a finite length he comes back to where he was. Now imagine you shrink his world along the up-down axis. And you make it smaller and smaller until pacman just barely fits in. Now he can stricty speaking still move "up" and "down" - but it doesn't matter. He is immediately in the same place. The world has become effectively 1 dimensional as the second dimension has been rolled up so far that it doesn't matter anymore as far as the movement of particles (like pacman) within it is concerned.