????????
      +---------
TVUHH | NHWHMNXG
       -VJLHX
        =====
        UWLHHN
       -UYPLHY
        ======
          ZGHHX
         -PRWHQ
          =====
          UGJRTG
         -UGUWHV
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard
attributes: nested indirection