NHR
      +--------
VWLHY | GTUUHNM
       -VWLHY
        =====
        RRMLJN
       -RXQTVY
        ======
         NGPXUM
        -NLVVQX
         ======
          PJPRM

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: medium
missing: Z