We show that the Lp norms, 0< p<∞, of the nontangenital maximal function and area integral of solutions and normalized adjoint solutions to second order nondivergence form elliptic equations, are comparable when integrated on the boundary of a Lipschitz domain with respect to measures, which are respectively A∞ with respect to the corresponding harmonic measure or normalized harmonic measure.
Both authors are supported by NSF
"Area integral estimates for solutions and normalized adjoint solutions to nondivergence form elliptic equations." Ark. Mat. 31 (2) 275 - 296, October 1993. https://doi.org/10.1007/BF02559487