[error] DEADLOCK/NODUP: no remaining values
[error] DEADLOCK/NODUP: no remaining values
        ????????
      +---------
C6518 | 20801774
       -C6518
        =====
        531367
       -502C31
        ======
         7A50C7
        -51C20B
         ======
          C41934
         -CCAB55
          ======
          ??????

base: 13
letters: 0123456789ABC
difficulty: hard