+ // The basic logic for visiting the neighbors of a user is to iterate the channel list of the user
+ // and visit all users on those channels. Because two users may share more than one common channel,
+ // we must skip users that we have already visited.
+ // To do this, we make use of a global counter and an integral 'already_sent' field in LocalUser.
+ // The global counter is incremented every time we do something for each neighbor of a user. Then,
+ // before visiting a member we examine user->already_sent. If it's equal to the current counter, we
+ // skip the member. Otherwise, we set it to the current counter and visit the member.