The aim of this paper is to establish symmetry and monotonicity of solutions to the equation involving fractional Laplacians of higher order. For this purpose, we first reduce the equation into a system via the composition of lower fractional Laplacians and then obtain symmetry and monotonicity of solutions to the system by applying the method of moving planes.
"Symmetry and monotonicity of solutions for equations involving the fractional Laplacian of higher order." Rocky Mountain J. Math. 48 (2) 485 - 499, 2018. https://doi.org/10.1216/RMJ-2018-48-2-485