Before moving on, test your understanding. If node is an ancestor of node , what is true about their entry and exit times?
Answer: tin[u] < tin[v] and tout[u] > tout[v]. The ancestor enters first and exits last. This property is the foundation for checking if one node is in another's subtree. If tin[u] <= tin[v] and tout[v] <= tout[u], then is in 's subtree. You will use this check constantly when working with Euler tours.