During the algorithm we maintain a potential y and an orientation of G_y (denoted by \overrightarrow{G_y}) which has the property that the edges oriented from T to S form a matching M. Initially, y is 0 everywhere, and all edges are oriented from S to T (so M is empty).
If R_T \cap Z is empty, then let \Delta := \min \{c(i,j)-y(i)-y(j): i \in Z \cap S, j \in T \setminus Z\}.