 0. Consider first node 0. Its contribution to the cut if added to set Y is σ Y (0) = ∑ u ∈ X w 0, u = w 0, 0 = 0. Since node 0 is not adjacent to node 0, the only node in Y, then σ X (0) = ∑ u ∈ Y w 0, u = 0. 