  A recent paper [M. H. Lee, Phys. Rev. Lett. 98, 190601 (2007)] has called
attention to the fact that irreversibility is a broader concept than
ergodicity, and that therefore the Khinchin theorem [A. I. Khinchin,
Mathematical Foundations of Statistical Mechanics (Dover, New York) 1949] may
fail in some systems. In this Letter we show that for all ranges of normal and
anomalous diffusion described by a Generalized Langevin Equation the Khinchin
theorem holds.
