PEG is a computer version of a "one-dimensional" pegboard solitaire game where your goal is to reverse the starting configuration of the pegs through the correct sequence of moves. The input scheme is simple: because any peg can only have one legal move at a given moment, you only have to tell the PET which peg you want to move. It's possible to get yourself into an unwinnable state but once you see the pattern, the solution makes sense and should be easy to reproduce. If you get stuck, you can have the PET play out the solution while you watch—a nice bit of finesse from the programmer.