@article{10_1090_S0894_0347_1990_1049696_6,
     author = {Grove, Karsten and Petersen, Peter},
     title = {A pinching theorem for homotopy spheres},
     journal = {Journal of the American Mathematical Society},
     pages = {671--677},
     publisher = {mathdoc},
     volume = {03},
     number = {3},
     year = {1990},
     doi = {10.1090/S0894-0347-1990-1049696-6},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-1990-1049696-6/}
}