9. The teacher gives a function $y=f(x)$, and four students, A, B, C, and D, each point out a property of this function: A: For $x \in \mathbf{R}$, $f(1+x)=f(1-x)$; B: The function is decreasing on $(-\infty, 0]$; C: The function is increasing on $(0,+\infty)$; D: $f(0)$ is not the minimum value of the function. If exactly three of them are correct, please write down such a function: $\qquad$
9. $y=(x-1)^{2}$ (answer is not unique).

