Figure 1.

(a) An example of a level-2 network N, (b) the tree bc(N), (c) a switching of N where the switched-off edges are dotted, (d) a network N' such that ${\mathcal{M}}_{N^{\prime }}\left(x,y\right)=\left\{m_{\mathsf{\text{1}}},m_{\mathsf{\text{2}}},m_{\mathsf{\text{3}}}\right\}$, (e) another switching of a network. Note that the edge (a; b) will also be switched off since all out-going edges of b are off.