@article{10_1090_S0894_0347_1990_1030656_6,
     author = {Abresch, Uwe and Gromoll, Detlef},
     title = {On complete manifolds with nonnegative {Ricci} curvature},
     journal = {Journal of the American Mathematical Society},
     pages = {355--374},
     publisher = {mathdoc},
     volume = {03},
     number = {2},
     year = {1990},
     doi = {10.1090/S0894-0347-1990-1030656-6},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-1990-1030656-6/}
}