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