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