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