The derivative of the derivative, if the derivative is increasing, that means the derivative of that must be positive. And it is indeed the case that the derivative is positive. And we have a word for this downward opening u and this upward opening u. We call this concave downwards. Let me make this clear. Concave downwards, and we call this concave upwards. So let's review how we can identify concave downward intervals and concave upwards intervals.