Determine whether the following rule defines $y$ as a function of $x$ \begin{tabular}{|c|c|c|c|c|c|c|c|} \hline$x$ & 9 & 4 & 1 & 0 & 1 & 4 & 9 \\ \hline$y$ & 3 & 2 & 1 & 0 & -1 & -2 & -3 \\ \hline \end{tabular} Is $y$ a function of $x$ ? Yes No

Step 1 ：Determine whether the following rule defines $y$ as a function of $x$

Step 2 ：In order for $y$ to be a function of $x$, each value of $x$ must correspond to exactly one value of $y$.

Step 3 ：Looking at the table, we can see that the values of $x$ are not unique - the values 9, 4, and 1 each appear twice, with different corresponding $y$ values.

Step 4 ：Therefore, $y$ is not a function of $x$.

Step 5 ：Final Answer: \(\boxed{\text{No}}\)