Fig. 4.

The 9 altruistic configurations in ${\mathbb{R}}^3$. Compared to $\mathrm{btm}(\rho )$ at depth k, the vertex $\lambda =\mathrm{last}(\rho )$ has depth $k-3$, $k-2$, and $k-1$ in the top, middle, and bottom row. Similarly, the slice is at depth $k-3$, $k-2$, and $k-1$ in the left, middle, and right column