????????
      +---------
LWGQJ | UGPWNUNU
       -LWGQJ
        =====
        WFNRFU
       - LWGQJ
        ======
         MHGQGN
        -MEEPHG
         ======
          HJUUPU
         -MLWNLU
          ======
          ??????

base: 13
letters: EFGHJLMNPQRUW
difficulty: medium