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