MZLY
      +---------
ZVYJG | PHRPYZGW
       -ZVYJG
        =====
        VQLJVZ
       -VGZQWL
        ======
         XZRZNG
        -XRUMZH
         ======
          GYXMXW
         -GRTJMP
          ======
           MYRYM

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard