Pentalpha is a puzzle where the goal is to place nine stones on the ten intersections of a pentagram. The puzzle is used as a confidence trick in Mexico, where it is known as estrella mágica.[1] The following rules need to be obeyed when placing the stones:
The stone has to visit two other points before reaching its final point.
These three points have to be next to each other.
The points have to be in a straight line.
Although the second (middle) point is allowed to be occupied by a stone, the first (starting) and third (ending) points must be clear before a stone is placed at the third (ending) point.
Solution
The solution to Pentalpha can be found for any starting point using the following algorithm: