vertices(g) = 0 1 2 3 4 
vertex id: 0
out-edges: (0,1) (0,2) (0,3) (0,4) 
in-edges: (2,0) (3,0) (4,0) 
adjacent vertices: 1 2 3 4 

vertex id: 1
out-edges: 
in-edges: (0,1) (3,1) (4,1) 
adjacent vertices: 

vertex id: 2
out-edges: (2,0) (2,4) 
in-edges: (0,2) 
adjacent vertices: 0 4 

vertex id: 3
out-edges: (3,0) (3,1) (3,4) 
in-edges: (0,3) 
adjacent vertices: 0 1 4 

vertex id: 4
out-edges: (4,0) (4,1) 
in-edges: (0,4) (2,4) (3,4) 
adjacent vertices: 0 1 

