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bool operator<(const Expression& other) const {        if (opcode < other.opcode)          return true;        else if (other.opcode > opcode)          return false;                if (lhs < other.lhs)          return true;        else if (other.lhs > lhs)          return false;                  if (rhs < other.rhs)          return true;        else if (other.rhs > rhs)          return false;                return false;      }