@article{SIGMA_2015_11_a42,
     author = {Robin Heinonen and Ernest G. Kalnins and Willard Miller Jr. and Eyal Subag},
     title = {Structure {Relations} and {Darboux} {Contractions} for {2D} 2nd {Order} {Superintegrable} {Systems}},
     journal = {Symmetry, integrability and geometry: methods and applications},
     year = {2015},
     volume = {11},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SIGMA_2015_11_a42/}
}