[(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),(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)]
