Díaz Díaz, Jesús IldefonsoDíaz Díaz, GregorioOtero Juez, Jesus2023-06-202023-06-202006-041468-121810.1016/j.nonrwa.2005.01.001https://hdl.handle.net/20.500.14352/49967We show the existence and uniqueness of a viscosity solution for an oblique nonlinear problem suggested by the study of the Backus problem on the determination of the external gravitational potential of the Earth from surface measurements of the modulus of the gravity force field.engjournal articlehttp://www.sciencedirect.com/science/article/pii/S1468121805000027http://www.sciencedirect.com/restricted access517.954elliptic-equationsharmonic-functionsuniquenessnonlinear oblique boundary value problemviscosity solutionsBackus problemgravity potentialEcuaciones diferenciales1202.07 Ecuaciones en Diferencias