[error] DEADLOCK/NODUP: no remaining values
        ????????
      +---------
494A2 | B9007687
       -494A2
        =====
        958066
       - 494A2
        ======
         398628
        -129705
         ======
          198A87
         -762A06
          ======
          ??????

base: 12
letters: 0123456789AB
difficulty: medium