By "system call", we do not mean "kernel call" but more "call to the system" in a broader sense, that is from the program to its environment (it could be the OS or other libraries). We should probably use another word since this is confusing.

More exactly, we check that the only calls when the user is not logged in are: ReadFile, ListPosts or Log: https://github.com/clarus/coq-chick-blog/blob/master/Spec.v#...