YYTX
      +---------
PVLLQ | ZTUJNJHG
       -PVLLQ
        =====
        YYQZVJ
       - PVLLQ
        ======
         WULXTH
        -WMWJNM
         ======
          QHXNPG
         -QZQJJG
          ======
           QGNZR

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