Hi,

My question is about the presentation of recitation number 9 in slide 26 : Let's call the vertices a-d from the vertex next to s clockwise i.e, the vertex next to s from up is a, and the vertex next to s from down is d. The vertex in the middle of the four vertices a-d is e. Why does the d vertex belongs to the S set (of the cut S-T)? It looks to me that d is unreachable from s in the residual network, since the edge (s,d) doesn't exist in the residual network, because it's saturated, and the edge (e,d) also doesn't exist since the residual capacity is equal to its capacity minus its flow which is equal to 0 - (-0), since the flow of (d,e) is equal to 0.

Where is my mistake?

Thank you very much! :)