@article{GDZPPN002438364, title = {An inverse problem of the wave equation.}, journal = {Mathematische Zeitschrift}, volume = {207}, year = {1991}, pages = {119-130}, zbl = {0697.35164}, url = {http://dml.mathdoc.fr/item/GDZPPN002438364} }
Sjöstrand, J.; Ramm, A.G. An inverse problem of the wave equation.. Mathematische Zeitschrift, Tome 207 (1991) pp. 119-130. http://gdmltest.u-ga.fr/item/GDZPPN002438364/