On the other hand , problems 1 , 2 , 5 , 9 , 15 , 18 + , and 22 have solutions that have partial acceptance , but there exists some controversy as to whether they resolve the problems .
On the other hand , problems 1 , 2 , 5 , 9 , 15 , 18 + , and 22 have solutions that have partial acceptance , but there exists some controversy as to whether it resolves the problem .