Departamento de Matemática, Universidade de Coimbra, Apartado 3008, 3000 Coimbra, Portugal ; Departamento de Matemática, Universidade de Coimbra, Apartado 3008, 3000 Coimbra, Portugal
Abstract:
It is proved that if a generalized Goursat-Darboux problem is -well posed then the operator cannot contain derivatives with respect to one of the variables.