????????
      +---------
GNUMF | MLTFLQFN
       -WQFUR
        =====
        UXQUNQ
       -URTYNX
        ======
         UQLPUF
        -URTYNX
         ======
          GLGGXN
         -GGMGML
          ======
          ??????

base: 13
letters: FGLMNPQRTUWXY
difficulty: hard