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