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