There has been considerable progress in recent years solving inverse problems for nonlinear hyperbolic equations. One of the striking aspects these developments is use nonlinearity to get new information, which not possible corresponding linear We illustrate this several examples including Einstein equations and elasticity among others.

In this note we prove a new symmetrization result, in the form of mass concentration comparison, for solutions nonlocal nonlinear Dirichlet problems involving fractional $ p Laplacians. Some regularity estimates will be established as direct application main result.