Singular solutions to Protter's problem for the 3-D wave equation involving lower order terms. Grammatikopoulos, Myron.K.; Hristov, Tzvetan D.; Popivanov, Nedyu I. — 2003 Electronic Journal of Differential Equations (EJDE) [electronic only]
On the singularities of 3-D Protter's problem for the wave equation. Grammatikopoulos, Myron K.; Hristov, Tzvetan D.; Popivanov, Nedyu I. — 2001 Electronic Journal of Differential Equations (EJDE) [electronic only]