????????
      +---------
PUZWV | TVGWTGHV
       -XQYJJ
        =====
        PJQJMG
       -PRHPRX
        ======
         PWHRVH
        -PMRLQZ
         ======
           LJXGV
          -TXXUP
           =====
           ?????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard
missing: N