@article{CRMATH_2012__350_7-8_355_0,
     author = {Nourrigat, Jean},
     title = {Closure of the set of pseudodifferential operators},
     journal = {Comptes Rendus. Math\'ematique},
     pages = {355--358},
     publisher = {Elsevier},
     volume = {350},
     number = {7-8},
     year = {2012},
     doi = {10.1016/j.crma.2012.04.006},
     language = {en},
     url = {http://www.numdam.org/articles/10.1016/j.crma.2012.04.006/}
}