A simple example of this would be the function $f(x) = \frac{1}{x-2}$, but we need to define $f(2)$ to be undefined. So, we can define our function as:
\[f(x) =
\begin{cases}
\frac{1}{x-2} & \text{if } x \neq 2 \\
\text{undefined} & \text{if } x = 2
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