????????
      +---------
ZHZMH | HXZLVRNP
       -ZHZMH
        =====
        ZZMVTR
       -ZGMQHN
        ======
          MYXLN
         -NUVXJ
          =====
          ZGUXXP
         - MQUWY
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard