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