@article{10_1090_S0894_0347_07_00578_4,
     author = {Popa, Sorin},
     title = {On the superrigidity of malleable actions with spectral gap},
     journal = {Journal of the American Mathematical Society},
     pages = {981--1000},
     publisher = {mathdoc},
     volume = {21},
     number = {4},
     year = {2008},
     doi = {10.1090/S0894-0347-07-00578-4},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-07-00578-4/}
}