EN
For two strictly elliptic operators L₀ and L₁ on the unit ball in ℝⁿ, whose coefficients have a difference function that satisfies a Carleson-type condition, it is shown that a pointwise comparison concerning Lusin area integrals is valid. This result is used to prove that if L₁u₁ = 0 in B₁(0) and $Su₁ ∈ L^{∞}(S^{n-1})$ then $u₁|_{S^{n-1}} = f$ lies in the exponential square class whenever L₀ is an operator so that L₀u₀ = 0 and $Su₀ ∈ L^{∞}$ implies $u₀|_{S^{n-1}}$ is in the exponential square class; here S is the Lusin area integral. The exponential square theorem, first proved by Thomas Wolff for harmonic functions in the upper half-space, is proved on B₁(0) for constant coefficient operator solutions, thus giving a family of operators for L₀. Methods of proof include martingales and stopping time arguments.