I was asking about the second derivative; if d(users)/dt wasn't constant, then d^2(users)/dt2 is nonzero and eternal september risk is fairly high (assuming HN

I was asking about the second derivative; if d(users)/dt wasn't constant, then d^2(users)/dt2 is nonzero and eternal september risk is fairly high (assuming HN isn't shrinking). If you assume idealized user growth (which doesn't happen -- there are so many people in the end that would care to either join HN or troll HN), then eternal september is actually guaranteed if d^2(users)/dt2 > 0, since there will come a time t when (new users) > (old users).