@article{COCV_2000__5__219_0,
     author = {Lebeau, Gilles},
     title = {The wave equation with oscillating density : observability at low frequency},
     journal = {ESAIM: Control, Optimisation and Calculus of Variations},
     pages = {219--258},
     publisher = {EDP-Sciences},
     volume = {5},
     year = {2000},
     mrnumber = {1750616},
     zbl = {0953.35083},
     language = {en},
     url = {http://www.numdam.org/item/COCV_2000__5__219_0/}
}