@article{10_4153_CMB_2011_134_0,
     author = {Pigola, S. and Rimoldi, M.},
     title = {Characterizations of {Model} {Manifolds} by {Means} of {Certain} {Differential} {Systems}},
     journal = {Canadian mathematical bulletin},
     pages = {632--645},
     year = {2012},
     volume = {55},
     number = {3},
     doi = {10.4153/CMB-2011-134-0},
     url = {http://geodesic.mathdoc.fr/articles/10.4153/CMB-2011-134-0/}
}