Rules: by pushing on the arrows, you turn 4 cubes at a time. Bring the puzzle into a form where each row has the same color. Mathematiclly speaking you play this game in a finitely presented group. It is a subgroup of the permutation group S16 which is generated by 9 permutations of order 4. The puzzle is much simpler than the Rubik cube puzzle.
For an introduction into the mathematical theory of finitely presented groups, see the book: G. Baumslag, 'Topics in combinatorial group theory, Birkäuser Verlag, Basel, 1993

©, 1999