[(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)]
[(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)]
