????????
      +---------
GLJUW | GPQTLRTX
       -GLJUW
        =====
         YLHTR
        -RUYQQ
         =====
         GGGQWT
        -GNPRFJ
         ======
           YWFUX
          -RUYQQ
           =====
           ?????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard
hints: M << J
missing: M