1. Approximation Taxonomy of Metric TSP (2015).
http://theory.cs.uni-bonn.de/info5/tsp
2. Asadpour, A., Goemans, M., Mądry, A., Gharan, S., Saberi, A.: An
$$O(\log n/ \log \log n)$$
O
(
log
n
/
log
log
n
)
-approximation algorithm for the asymmetric traveling salesman problem. In: Proceedings of the 21st SODA, pp. 379–389 (2010)
3. Lecture Notes in Computer Science;P Berman,1999
4. Berman, P., Karpinski, M.: Efficient amplifiers and bounded degree optimization. ECCC TR01-053 (2001)
5. Berman, P., Karpinski, M.: Improved approximation lower bounds on small occurrence optimization. ECCC TR03-008 (2003)