@article{SIGMA_2010_6_a10,
     author = {Jean-Pierre Gazeau and Petr Siegl and Ahmed Youssef},
     title = {Krein {Spaces} in de {Sitter} {Quantum} {Theories}},
     journal = {Symmetry, integrability and geometry: methods and applications},
     year = {2010},
     volume = {6},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SIGMA_2010_6_a10/}
}