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