GPL
      +---------
QYLQR | GENWGPJF
       -LQEPYL
        ======
         PJFRWJ
        -EYYFPJ
         ======
          LYEYMF
         -JQNRYF
          ======
           YYRLM

base: 13
letters: EFGJLMNPQRWXY
difficulty: medium
restrictions: no multiplication
missing: X