Re: [math-fun] 15-puzzle

I'm surprised that the 4x4 case hasn't been solved - can anyone help? NJAS Why is this surprising? There are more than 2e13 configurations. If we could search a thousand configurations per second, considering each of them would take almost a millennium. So, someone will have to do some non-trivial theory in order to get a better handle on the diameter of the 15-puzzle. I believe the diameter of Rubik's Cube is also not known, in any of the popular metrics. -A