@article{CRMATH_2009__347_1-2_63_0,
     author = {Mehrenberger, Michel},
     title = {An {Ingham} type proof for the boundary observability of a $ N-d$ wave equation},
     journal = {Comptes Rendus. Math\'ematique},
     pages = {63--68},
     publisher = {Elsevier},
     volume = {347},
     number = {1-2},
     year = {2009},
     doi = {10.1016/j.crma.2008.11.002},
     language = {en},
     url = {http://www.numdam.org/articles/10.1016/j.crma.2008.11.002/}
}