[error] DEADLOCK/NODUP: no remaining values
        ????????
      +---------
AA911 | 8A4C6995
       -AA911
        =====
        0B64C9
       - AA911
        ======
         676429
        -93815C
         ======
          7C7585
         -4ACB95
          ======
          ??????

base: 13
letters: 0123456789ABC
difficulty: medium