1. Agrawal A, Klein P, Ravi R (1991) When trees collide: an approximation algorithm for the generalized Steiner problem on networks. In: Proceedings of the 23rd annual ACM symposium on theory of computing. Association for Computing Machinery, New York, pp 134–144
2. Agrawal A, Klein P, Ravi R (1995) When trees collide: an approximation algorithm for the generalized Steiner problem in networks. SIAM J Comput 24(3):445–456
3. Aneja YP (1980) An integer linear programming approach to the Steiner problem in graphs. Networks 10(2):167–178
4. Arora S, Lund C, Motwani R, Sudan M, Szegedy M (1998) Proof verification and the hardness of approximation problems. J ACM 45(3):501– 555
5. Awerbuch B, Azar Y, Bartal Y (1996) On-line generalized Steiner problem. In: Proceedings of the 7th annual ACM-SIAM symposium on discrete algorithms, 2005. Society for Industrial and Applied Mathematics, Philadelphia, pp 68–74