@article{SIGMA_2008_4_a3,
     author = {Juha Pohjanpelto and Stephen C. Anco},
     title = {Generalized {Symmetries} of {Massless} {Free} {Fields} on {Minkowski} {Space}},
     journal = {Symmetry, integrability and geometry: methods and applications},
     year = {2008},
     volume = {4},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SIGMA_2008_4_a3/}
}