NUG
      +--------
PLMWU | HGHGJNX
       -PLMWU
        =====
        NRWFMN
       -NYFMTJ
        ======
         QUQMMX
        -QPUWNP
         ======
          PLJYP

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard