@article{SIGMA_2017_13_a20,
     author = {D. L. Ferrario},
     title = {Central {Configurations} and {Mutual} {Differences}},
     journal = {Symmetry, integrability and geometry: methods and applications},
     year = {2017},
     volume = {13},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SIGMA_2017_13_a20/}
}