????????
      +---------
FJJLU | QUNQXPRL
       -FJJLU
        =====
        JXMPRP
       -JQRHQM
        ======
         HERJXR
        -HFWHXX
         ======
          HRMWHL
         -HLJEEL
          ======
          ??????

base: 13
letters: EFHJLMNPQRUWX
difficulty: hard
hints: W << N