@article{CRMATH_2007__344_11_681_0,
     author = {Kuhlmann, Salma and Putinar, Mihai},
     title = {Positive polynomials on fibre products},
     journal = {Comptes Rendus. Math\'ematique},
     pages = {681--684},
     publisher = {Elsevier},
     volume = {344},
     number = {11},
     year = {2007},
     doi = {10.1016/j.crma.2007.04.009},
     language = {en},
     url = {http://www.numdam.org/articles/10.1016/j.crma.2007.04.009/}
}