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