In this illustration, we see four routers in a diamond shape. The top of the diamond is router W, the right side of the diamond is router X, the bottom of the diamond is router Y, and the left side of the diamond is router Z. Routers Z and X are further labeled with 1s, while router Y is further labeled with a lowercase E. A blue arrow pointing from Z to W (running clockwise) is labeled 1. Meanwhile, a blue arrow pointing from Z to Y (running counter-clockwise) is labeled 0, from Y to X is labeled e, and from X to W is labeled 1 + e. Blue arrows pointing from X to Y and from Y to Z are labeled 0.