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