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