????????
      +---------
PJJHN | UMUMXNNQ
       -PJJHN
        =====
        FRTUHN
       -FGPHQP
        ======
         RHFUQN
        -RGMTUM
         ======
          YFJRYQ
         -NXNGQX
          ======
          ??????

base: 13
letters: FGHJMNPQRTUXY
difficulty: hard