When the teacher randomly checks the attendance, the double is there to say "present!" when Cheng's name is called.
老师随机检查出席率时，每当点到程明的名字，替身就会提他喊到。
2
The system then automatically registers that the baggage is lost and double-checks the passenger contact details in order to notify them when the baggage resurfaces.
Double spending and (probably short-duration) expiration checks further assure sincere interest in the edit. It was not difficult for me to generate the above URL using the command.