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