The criteria wasn't "no repeating" digits -- just " not all repeating." In other words, you can't use 1111,2222,3333,4444,5555,6666,7777,8888, or 9999 for obvious reasons (the largest and smallest numbers would be the same and so the first subtraction would yield zero). But any other 4-digit combination should work -- so 1112 or 1311 or whatever would be fine.