Surface $X_2$ (step-by-step)
$$G_S=\begin{bmatrix}4 & 0 & 0\\ 0 & -2 & 0\\0 & 0 & -2\end{bmatrix}$$
Wehler $K3$ surface (step-by-step)
$$G_S =\begin{bmatrix}0 & 2 & 2 \\ 2 & 0 & 2 \\ 2 & 2 & 0 \end{bmatrix}$$
Surface $X_2$ (step-by-step)
$$G_S=\begin{bmatrix}4 & 0 & 0\\ 0 & -2 & 0\\0 & 0 & -2\end{bmatrix}$$
Wehler $K3$ surface (step-by-step)
$$G_S =\begin{bmatrix}0 & 2 & 2 \\ 2 & 0 & 2 \\ 2 & 2 & 0 \end{bmatrix}$$