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