  The fractional laplacian is an operator appearing in several evolution models
where diffusion coming from a L\'evy process is present but also in the
analysis of fluid interphases. We provide an extension of a pointwise
inequality that plays a r\^ole in their study. We begin recalling two scenarios
where it has been used. After stating the results, for fractional
Laplace-Beltrami and Dirichlet-Neumann operators, we provide an sketch of their
proofs, unravelling the underlying principle to such inequalities.
