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