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