1. The Traveling Salesman Problem and Its Variations, Ed. by G. Gutin and A. P. Punnen (Springer, Berlin, 2002).
2. J. W. Cook, In Pursuit of the Traveling Salesman: Mathematics at the Limits of Computation (Princeton Univ. Press, Princeton, 2012).
3. E. Kh. Gimadi and M. Yu. Khachai, Extremal Problems on Sets of Permutations (Izd. UMTs UPI, Yekaterinburg, 2016) [in Russian].
4. I. I. Melamed, S. I. Sergeev, and I. Kh. Sigal, “The traveling salesman problem. Issues in the theory,” Automat. Remote Control 50 (9), 1147–1173 (1989).
5. I. I. Melamed, S. I. Sergeev, and I. Kh. Sigal, “The traveling salesman problem. Exact methods,” Automat. Remote Control 50 (10), 1303–1324 (1989).