[error] DEADLOCK/NODUP: no remaining values
        ????????
      +---------
353DD | 3E7ACDE1
       -353DD
        =====
         8878D
        -404BB
         =====
          5389E
         -1E1B6
          =====
           509A1
          -1E1B6
           =====
           ?????

base: 15
letters: 0123456789ABCDE
difficulty: hard
hints: 5 << D
missing: 2