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