@article{SIGMA_2008_4_a35,
     author = {Stephen M. Paneitz},
     title = {A~Quartic {Conformally} {Covariant} {Differential} {Operator} for {Arbitrary} {Pseudo-Riemannian} {Manifolds} {(Summary)}},
     journal = {Symmetry, integrability and geometry: methods and applications},
     year = {2008},
     volume = {4},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SIGMA_2008_4_a35/}
}