Let \Tᶻ\ be an ergodic action of the group Zⁿ by automorphisms of the probability space (X, m), ₈^ aᵢ0. For any sequence Mₖ + there exist Nₖ>Mₖ and a function f L₁ (X, m) such that m (\ x: \ |\, A (x, Nₖ, f) - f \, dm\, |\ >\ aₖ \) \ \ 1, where A (x, N, f) = 1 Nⁿ ₙ ₐ₍ f (T^zx), QN=\ (z₁, , zₙ) \\,: \, 1 z₁, , zₙ N\}.
Valery V. Ryzhikov (Tue,) studied this question.