Worlds Hardest 15-Puzzle

Worlds Hardest 15-Puzzle This is a surprinsing version of the 15-puzzle game I found in my great-great-great-grandfathers trunk. Whereas the original 140 years old game has its 15 pieces numbered from 1 to 15 (hence its name), this one has no numbers, all pieces are the same. At first I wondered what kind of joke this was, with its boasting "Worlds Hardest 15-puzzle"? All pieces are identical, games resolved! That is, until I began fiddling with it and saw some pieces lighting on! Then I figured each piece has its intended place where it lights up, and the games done once all pieces shine. I a...