MFG
      +--------
LMPGN | UMJJLGG
       -UQPHR
        =====
         WUHNG
        -JMGJM
         =====
         LNGTJG
        -LNQRGP
         ======
           UTPF

base: 13
letters: FGHJLMNPQRTUW
difficulty: medium
missing: F