????????
      +---------
RWURW | WHWGHRGG
       -RWURW
        =====
        JTCCTR
       -JGUJGU
        ======
         HCRHRG
        -HRUHRU
         ======
          JRUUGG
         -JGUJGU
          ======
          ??????

base: 12
letters: CFGHJLMNRTUW
missing: F L M N
difficulty: challenging
hints: F < N, M < J