????????
      +---------
FWUFN | TRLXWXFU
       -FWUFN
        =====
        YERUJX
       -XUFPWP
        ======
         JFULYF
        -JJXYET
         ======
          XRNXMU
         -XNRYFL
          ======
          ??????

base: 13
letters: EFJLMNPRTUWXY
difficulty: hard