@article{MM2_1987__58_155208,
     author = {Alfredo Brega and Juan Tirao},
     title = {K-Invariants in the universal enveloping algebra of the {Desitter} {Group.}},
     journal = {Manuscripta mathematica},
     pages = {1--36},
     publisher = {mathdoc},
     volume = {58},
     year = {1987},
     zbl = {0636.17004},
     url = {http://geodesic.mathdoc.fr/item/MM2_1987__58_155208/}
}