FEPF
      +---------
FPXMT | XFMFEGUF
       -FPXMT
        =====
         HWLGG
        -TRGRU
         =====
          HNTXU
         -HGWHM
          =====
           FPTPF
          -FPXMT
           =====
             EXT

base: 13
letters: EFGHLMNPRTUWX
difficulty: medium