????????
      +---------
XMPRW | WNTTULNV
       -XMPRW
        =====
        PHYGRL
       -PRYGXL
        ======
         XQQMQN
        -PJMPQG
         ======
          MJJTYV
         -MJGVGP
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard
hints: V << U
missing: Z