A. Archer, M. Bateni, M. Hajiaghayi, and H. Karloff, Improved Approximation Algorithms for Prize-Collecting Steiner Tree and TSP, SIAM Journal on Computing, vol.40, issue.2, pp.309-332, 2011.
DOI : 10.1137/090771429
URL : http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.158.5280

C. Bazgan, B. Couëtoux, and Z. Tuza, Complexity and approximation of the Constrained Forest problem, Theoretical Computer Science, vol.412, issue.32, pp.4081-4091, 2011.
DOI : 10.1016/j.tcs.2010.07.018

J. Byrka, F. Grandoni, T. Rothvoß, and L. Sanitá, An improved LP-based approximation for steiner tree, Proceedings of the 42nd ACM symposium on Theory of computing, STOC '10, pp.583-592, 2010.
DOI : 10.1145/1806689.1806769

B. Couëtoux, A $\frac{3}{2}$ Approximation for a Constrained Forest Problem, In: C. Demetrescu, M.M
DOI : 10.1007/978-3-642-23719-5_55

M. X. Goemans and D. P. Williamson, Approximating minimum-cost graph problems with spanning tree edges, Operations Research Letters, vol.16, issue.4, pp.183-189, 1994.
DOI : 10.1016/0167-6377(94)90067-1

M. X. Goemans and D. P. Williamson, A General Approximation Technique for Constrained Forest Problems, SIAM Journal on Computing, vol.24, issue.2, pp.296-317, 1995.
DOI : 10.1137/S0097539793242618

M. X. Goemans and D. P. Williamson, The primal-dual method for approximation algorithms and its application to network design problems Approximation Algorithms for NP-hard Problems, 1996.

C. Imieli´nskaimieli´nska, B. Kalantari, and L. Khachiyan, A greedy heuristic for a minimum-weight forest problem, Operations Research Letters, vol.14, issue.2, pp.65-71, 1993.
DOI : 10.1016/0167-6377(93)90097-Z

J. Kruskal, On the shortest spanning subtree of a graph and the traveling salesman problem, Proceedings of the American Mathematical Society, vol.7, issue.1, pp.48-50, 1956.
DOI : 10.1090/S0002-9939-1956-0078686-7

M. Laszlo and S. Mukherjee, Another greedy heuristic for the constrained forest problem, Operations Research Letters, vol.33, issue.6, pp.629-633, 2005.
DOI : 10.1016/j.orl.2004.11.010

M. Laszlo and S. Mukherjee, A class of heuristics for the constrained forest problem, Discrete Applied Mathematics, vol.154, issue.1, pp.6-14, 2006.
DOI : 10.1016/j.dam.2005.06.006

M. Laszlo and S. Mukherjee, An approximation algorithm for network design problems with downwards-monotone demand functions, Optimization Letters, vol.3, issue.6, pp.171-175, 2008.
DOI : 10.1007/s11590-007-0051-8