The function \( f \) is defined below. \[ f(x)=\frac{x-1}{x^{2}-2 x+1} \] Find all values of \( x \) that are NOT in the domain of \( f \). If there is more than one value, separate them with commas.

1. The given function is \[ f(x)=\frac{x-1}{x^{2}-2x+1}. \] 2. To find values of \( x \) not in the domain, we need to determine when the denominator is equal to 0, since division by zero is not allowed. 3. Factor the denominator: \[ x^{2}-2x+1 = (x-1)^2. \] 4. Set the denominator equal to 0 and solve for \( x \): \[ (x-1)^2=0. \] Taking the square root of both sides gives: \[ x-1=0. \] Therefore: \[ x=1. \] 5. The value of \( x \) that is not in the domain of \( f \) is \( 1 \).