$pt(2)\Leftrightarrow y(x-1)-(x-1)=0\Leftrightarrow \left[ \begin{array}{l} x=1\\ y=1 \end{array} \right.$$\bullet x=1\Leftrightarrow \left[ \begin{array}{l} y=1\\ y=-2 \end{array} \right.$
$\bullet y=1\Leftrightarrow \left[ \begin{array}{l} x=1\\ x=-1 \end{array} \right.$
$S=\left\{ (1;1),(1;-2),(-1,1)\right\}$