@article{EJDE_2010__2010__a284,
     author = {Nicklason,  Gary R.},
     title = {Constant invariant solutions of the {Poincar\'e} center-focus problem},
     journal = {Electronic journal of differential equations},
     year = {2010},
     volume = {2010},
     zbl = {1218.34033},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EJDE_2010__2010__a284/}
}