????????
      +---------
TNQQL | GPLXNRNV
       -GYQQX
        =====
         WLVJR
        -TNQQL
         =====
         TUVJGN
        -RZZQLM
         ======
          XTHYWV
         -XYTQZJ
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard