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