???????
      +--------
WYYUW | JYUXHWP
       -XJJMH
        =====
        WJFGTW
       -WXYRFR
        ======
          RMFJP
         -RTWWF
          =====
          ?????

base: 13
letters: FGHJMNPRTUWXY
difficulty: medium
hints: G << N
missing: N