Computing a coverage union for the Hx y depicted in Fig. 3: gray vertex is sx y .
(a) An example of diagonal edge removal (broken lines would be removed).
(b) Hˆx y : vertices of Hˆx y are black points and a subset of Eˆ x y are arrows (it depicts only three connected components which are our concern; other directed edges of Hˆx y are omitted in the figure for simplicity).
(c) Heavy gray lines are the edges corresponding to the connected component with gray arrows in
(b) (broken lines would be removed after the refining step).