????????
      +---------
GUWPW | XTUNTGGH
       -GUWPW
        =====
        ZLZRMG
       -WGVNTJ
        ======
         RWUTNG
        -MNXWTV
         ======
          ZGMQGH
         -ZWGQLV
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard
hints: H+L=X
missing: Y