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