QTM
      +--------
ZUMTL | LZVWMHH
       -ZUMTL
        =====
        QHQPPH
       -QNYVMT
        ======
          TYNVH
         -WJLRX
          =====
          QNWVM

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