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