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