[error] DEADLOCK/NODUP: no remaining values
        6B7B
    +-------
059 | C61624
     -226
      ===
      9786
     -9B4B
      ====
       6B52
      -6867
       ====
        9234
       -9B4B
        ====
         691

base: 13
letters: 0123456789ABC
difficulty: hard
missing: A