[(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),(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)]
