Fig. 2.

Consistent sub-graphs of an ontology $\mathcal{O}=(V,E)$ with $\left|V\right|=7$ vertices and $\left|E\right|=7$ edges, shown in the upper left-hand corner. There are 15 consistent sub-graphs of $\mathcal{O}$, as shown by coloring the appropriate groups of vertices in blue (the first graph represents the ontology and the empty sub-graph at the same time). Observe that the reversal of all edges in the graph would lead to a reversed graph with the same number of consistent sub-graphs (white vertices; Theorem 5.1)