GTTE
      +---------
MLLWP | UHLQUHGU
       -MLLWP
        =====
        WWFHPH
       -GXHMLW
        ======
         WNFQLG
        -GXHMLW
         ======
          NNWXXU
         -TXENGN
          ======
           NHMQE

base: 13
letters: EFGHLMNPQTUWX
difficulty: medium
restrictions: no multiplication