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