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@article{PORMA_1959__18_2_114816, author = {Miles, E.P. jr.}, title = {The analytic {Cauchy} problem for the iterated wave equation}, journal = {Portugaliae mathematica}, pages = {111--119}, publisher = {mathdoc}, volume = {18}, number = {2}, year = {1959}, mrnumber = {0113041}, zbl = {0100.08901}, language = {en}, url = {http://geodesic.mathdoc.fr/item/PORMA_1959__18_2_114816/} }
Miles, E.P. jr. The analytic Cauchy problem for the iterated wave equation. Portugaliae mathematica, Tome 18 (1959) no. 2, pp. 111-119. http://geodesic.mathdoc.fr/item/PORMA_1959__18_2_114816/