NMFN
      +---------
NNMMU | MEXHEJHT
       -EEFUJ
        =====
         PGEGJ
        -FPYHH
         =====
         YJHMXH
        -YGUNXX
         ======
           MNPFT
          -EEFUJ
           =====
            UYUE

base: 13
letters: EFGHJMNPQTUXY
difficulty: hard
restrictions: no multiplication
missing: Q