Eden Chlamtác, Michael Dinitz, Guy Kortsarz, Bundit Laekhanukit. Approximating Spanners and Directed Steiner Forest: Upper and Lower Bounds. In Philip N. Klein, editor, Proceedings of the Twenty-Eighth Annual ACM-SIAM Symposium on Discrete Algorithms, SODA 2017, Barcelona, Spain, Hotel Porta Fira, January 16-19. pages 534-553, SIAM, 2017. [doi]
Abstract is missing.