QQPY
      +---------
VJVGQ | TMHYUZPP
       -VJVGQ
        =====
         XWMHZ
        -VJVGQ
         =====
         YJUNNP
        -YWXMLP
         ======
          QZPZRP
         -QNMTWY
          ======
           QYQYM

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard