[(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),(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)]
