Tree: (root) has children and . Node has child . DFS walk: Enter (tin[1]=0, timer becomes ), enter (tin[2]=1, timer becomes ), enter (tin[4]=2, timer becomes ), exit (tout[4]=3), exit (tout[2]=3), enter (tin[3]=3, timer becomes ), exit (tout[3]=4), exit (tout[1]=4).
Subtree of covers . Subtree of covers . Notice values are unique while values repeat (tout[4]=tout[2]=3).