????????
      +---------
LQLVP | JWPQJTVN
       -QYHMP
        =====
        TRXLZT
       -TWNVXG
        ======
         TVGWTV
        - YPJQG
         ======
          LMPMVN
         -LRPXWP
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard
missing: U