QFPF
      +---------
PMUJG | FYRUJLUF
       -PMUJG
        =====
        QTNWYL
       -QRPNHJ
        ======
         QMHWWU
        -QWXHUY
         ======
          QNTPWF
         -QRPNHJ
          ======
           WWJTJ

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard