EN
The rate of growth of an operator T satisfying the mean ergodic theorem (MET) cannot be faster than linear. It was recently shown (Kornfeld-Kosek, Colloq. Math. 98 (2003)) that for every γ > 0, there are positive L¹[0,1] operators T satisfying MET with $lim_{n→ ∞}||Tⁿ||/n^{1-γ} = ∞$. In the class of positive L¹ operators this is the most one can hope for in the sense that for every such operator T, there exists a γ₀ > 0 such that $lim sup||Tⁿ||/n^{1-γ₀} = 0.$ In this note we construct an example of a nonpositive L¹ operator with the highest possible rate of growth, that is, $lim sup_{n → ∞}||Tⁿ||/n > 0$.