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2. Finkel’štejn, Ju. Ju.: Näherungsverfahren und Anwendungsprobleme der diskreten Optimierung (Russian), Moscow 1976.
3. Korbut, A. A., und J. J. Finkelstein: Diskrete Optimierung, Berlin 1971. (Translated from Russian.)
4. Hansen, K. H., and J. Krarup: Improvements of the Held-Karp-algorithm for the symmetric Traveling Salesman Problem, Math. Progr. 7 (1974), 87–96.
5. Held, M., and R. M. Karp: The Traveling Salesman Problem and minimum spanning trees, Operations Res. 18 (1970), 1138–1162.