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