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