Game Modes

Level wrapping
Level wrapping causes an object moving outside the level to appear on the opposite side. A popular example of this is Pacman. This can be easily implemented by surrounding the level in some kind of  object and then using the following rule:

[ Border | < A | ... | | Border ] -> [ Border | | ... | A | Border ]

An  object wanting to move into a   object will be removed and placed adjacent to the nearest   in the opposite direction.