1. A. Bouchet. Greedy algorithm and symmetric matroids. Math. Programming, 38:147–159, 1987.
2. R. Chandrasekaran and S. N. Kabadi. Pseudomatroids. Discrete Math., 71: 205–217, 1988.
3. Lecture Notes in Comput. Sci.;J. Cheriyan,1998
4. R. Diestel. Graph Theory. Number 173 in Graduate Texts in Mathematics. Springer-Verlag, New York, 2nd edition, 2000.
5. M. X. Goemans, A. V. Goldberg, S. Plotkin, D. Shmoys, É. Tardos, and D. P. Williamson. Improved approximation algorithms for network design problems. In Proc. 5th Annual ACM-SIAM Symp. on Discrete Algorithms, pages 223–232, 1994.