Fig. 2.

Partitions and splitting. A partition is shown schematically, with a graph made up of two disjoint subgraphs, $V_0$ (white) and $V_1$ (gray), whose individual structures can be arbitrary, as suggested by the “cloud” outlines, with magenta edges splitting $V_0$ from $V_1$, blue edges splitting $V_1$ from $V_0$, and labels omitted for clarity.