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Let ''G'' be a graph that is [[Rigid graph|rigid]] in two dimensions-dimensional space. Can we determine in polynomial time the minimum number of edges whose deletion from ''G'' results in a graph which is not rigid?
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<ref name="Whi">W. Whiteley, ''Some matroids from discrete applied geometry'', in Contemporary Mathematics, J. G. Oxley, J. E. Bonin and B. Servatius, Eds., vol. 197. American Mathematical Society, 1996, [http://www.researchgate.net/publication/239568905_Some_matroids_from_discrete_applied_geometry ResearchGate link]</ref>
<ref name="LeSt">A Lee, I Streinu, ''Pebble game algorithms and sparse graphs'', Discrete Mathematics 308 (2008), 1425-1437. [http://dx.doi.org/10.1016/j.disc.2007.07.104 DOI link], [http://arxiv.org/abs/math/0702129 arXiv link].</ref>
<ref name="McC">S.T. McCormick, ''A Combinatorial Approach to Some Sparse Matrix Problems'', Ph.D. Thesis, Stanford University, Stanford CA (1983), [http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA131387 pdf link]</ref>
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