????????
      +---------
NEFJM | ULLFFPMQ
       -UWQFQ
        =====
         UNLJP
        -NEFJM
         =====
         NUWLJM
        -NFQLPF
         ======
           MXNWQ
          -JUYXW
           =====
           ?????

base: 13
letters: EFGJLMNPQUWXY
difficulty: hard
missing: G