????????
      +---------
XGPQT | NYEFMPFP
       -XGPQT
        =====
        FPTGEP
       -FHGWWR
        ======
         PXPFWF
        -PHNMTQ
         ======
          PTXEGP
         -PXWFTY
          ======
          ??????

base: 13
letters: EFGHMNPQRTWXY
difficulty: challenging
hints: X << Y, E << W