????????
      +---------
PNUTQ | QRVHPUZM
       -PNUTQ
        =====
        NXTUWU
       -NPXMVU
        ======
         TZHPGZ
        -TRWVXT
         ======
          NHRURM
         -NRULMJ
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard
hints: L << H, P << L
missing: Y