So over here, f prime of x2 is not defined. Let me just write undefined. So we have an interesting, and once again, I'm not rigorously proving it to you. I just want you to get the intuition here. We see that if we have some type of an extrema, and we're not talking about when x is at an endpoint of an interval. Just to be clear what I'm talking about when I'm talking about x as an endpoint of an interval. We're saying, let's say that the function is, let's say we have an interval from there.