????????
      +---------
VQWZJ | JVYPQHTV
       -UMLNQ
        =====
        VMPXMH
       - TUWRQ
        ======
         VJWYWT
        -VUNZVJ
         ======
           QNJXV
          -PGLTJ
           =====
           ?????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard
attributes: beautiful deep indirection