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