@article{10_1090_S0894_0347_2010_00687_X,
     author = {Hatami, Hamed and Norine, Serguei},
     title = {Undecidability of linear inequalities in graph homomorphism densities},
     journal = {Journal of the American Mathematical Society},
     pages = {547--565},
     publisher = {mathdoc},
     volume = {24},
     number = {2},
     year = {2011},
     doi = {10.1090/S0894-0347-2010-00687-X},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-2010-00687-X/}
}