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