# Optimal TSP Path with Branch and Bound

I just wanted a bit of clarification on the above picture. I understand the general idea of building out a tree in DFS order and stopping once you come across a number bigger than you got before. For example, when the value of the path becomes $$14$$ or $$inf$$ the algorithm stops because there was already a path of value $$11$$. But, I am quite confused with regards to where these numbers are coming from (the lower bounds on the cost). For example, the path from vertex $$A$$ to vertex $$B$$ has length $$1$$, but in the tree, the path from $$A$$ to $$B$$ has a lower bound of $$10$$.

So, I would greatly appreciate if anyone could let me know where the numbers in the branch-and-bound search tree are coming from!