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