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