UNTQ
      +---------
MLYRT | GZPJZTVY
       -YRPNJ
        =====
        RPHVQT
       -RHVRMX
        ======
         MPQWUV
        -MNUPXR
         ======
          NPXMQY
         -NRJWRZ
          ======
           WTRLW

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: challenging