????????
      +---------
YXLRN | LRPWUPUR
       -YXLRN
        =====
        YWFGWP
       -YHMLXN
        ======
         YYLNLU
        -YTYPPJ
         ======
          YTQJMR
         -YTYPPJ
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard