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