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