Your code is correct. The only problem is that you are printing the array b each time, instead of adding it to a list of lists (which should be your answer). And in the end you should return the list of lists, not the string "This cube is done".

Please read this: https://docs.codewars.com/training/troubleshooting#expected-the-same and this: https://docs.codewars.com/training/troubleshooting#post-discourse