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<references>
<ref name="BeVe">L. A. Végh, A. A. Benczúr, ''Primal-dual approach for directed vertex connectivity augmentation and generalizations'', [http://doi.acm.org/10.1145/1361192.1361197 DOI link], [http://www.cs.elte.hu/~veghal/papers/benczur-vegh-08.pdf Author link]</ref>
<ref name="JaJo">B. Jackson, T. Jordán, ''Independence free graphs and vertex connectivity augmentation'', [http://dx.doi.org/10.1016/j.jctb.2004.01.004 DOI link], [http://www.cs.elte.hu/egres/tr/egres-01-04.pdf EGRES Technical Report].</ref>
