[(0,1),(1,2),(1,3),(2,4),(3,5),(4,6),(2,7),(0,8),(7,8),(7,9),(3,10),(6,11),(9,12),(5,13),(4,14),(9,15),(5,16),(10,17),(6,18),(8,19),(10,20)]
[(0,1),(1,2),(2,3),(1,4),(3,5),(0,6),(4,7),(5,8),(2,8),(3,9),(6,10),(9,11),(5,12),(7,13),(7,14),(4,15),(8,16),(10,17),(9,18),(10,19),(6,20)]
