[(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),(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)]
