Instruct: Classify the given review as either positive or negative.
Query: intermediate difficulty: good as an exercise after Ruben cube

If you know how to solve Ruben cube, and more importantly, how to find a solution to Ruben cube, this puzzle is much easier. Still it can take about half an hour to come with a complete solution. So it is a fun. The common thing it shares with Ruben cube is that both are about finite permutation groups. Searching for a solution usually starts with repetitative application of a fix permutation, which would equal identity. Then perturb the permutation a bit to get a simple generator of the group.If you have not touched Ruben cube, this can be served as an introduction to brain teasers based on permutation groups.Forget abstract mathematics in the game. It is still enjoying. But people may lose interest after unsuccessful attemps without "theoretical" guidance.