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