[(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),(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)]
