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### Dynamic setting:
One of the motivations for the suggested framework is related to the dynamic nature of the reachability graph. However, the suggested framework does not seem to be particularly effective in a dynamic setting (need to recompute the sets "S" from scratch if the reachability graph is modified).
Recent work is dedicated to solving the k-center problem in a dynamic setting: "Fully Dynamic k-Center Clustering, Chan et al., WWW2018". The "asymmetric k-center problem" being a subproblem solved in the suggested framework, a more efficient algorithm in a dynamic setting seems possible.
### Effectiveness of greedy:
Nice to see that the greedy heuristic leads to a very good approximation on real-world instances for the considered problem (the exact result is known solving an integer program). On the contrary, an algorithm (Ullman and Yannakakis) having good theoretical guarantees performs poorly on the same real-world instances.
### Typos:
- "In Table 6.4, the column labeled...": should be "In Table 2, ..."

## Comments: