@article{10_1090_S0894_0347_08_00613_9,
     author = {Brendle, Simon and Schoen, Richard},
     title = {Manifolds with 1/4-pinched curvature are space forms},
     journal = {Journal of the American Mathematical Society},
     pages = {287--307},
     publisher = {mathdoc},
     volume = {22},
     number = {1},
     year = {2009},
     doi = {10.1090/S0894-0347-08-00613-9},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-08-00613-9/}
}