We return to the example of subsection II.B with $\mu = 1$, i.e.,
$$A(1) = \left(\begin{array}{ccc} 1 & -1 & 1 \\ -1 & 1 & 0 \\ 0 & -1 & 1 \end{array}\right)$$
How should we choose $N^{\prime} = \left(\begin{array}{ll} N_{1}^{\prime} & N_{2}^{\prime} \end{array}\right)$ so that $\operatorname{det}\left(N^{\prime\top} A N^{\prime}\right) = 0$?