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