????????
      +---------
GNTYJ | MPJXMPHN
       -WTZXY
        =====
        YUQVWP
       -YXPUUL
        ======
         LPJLQH
        -LQUHLR
         ======
          LLTHZN
         -LVQWMG
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: challenging