[error] DEADLOCK/NODUP: no remaining values
        ????????
      +---------
B9922 | 8868B419
       -B9922
        =====
        530C84
       -4281C9
        ======
         926261
        -981379
         ======
          B4D609
         -9A78A5
          ======
          ??????

base: 14
letters: 0123456789ABCD
difficulty: medium