title: Comment on "Quantum electrodynamic treatment of harmonic generation in intense optical fields"
authors.affiliation: CCAST (World Laboratory) P.O. Box 8730, Beijing 10080, China and Institute of Theoretical Physics Chinese Academy of Science P.O. Box 2735, Beijing 10080, China.
authors.initials: J
authors.lastname: Chen
authors.initials: SG
authors.lastname: Chen
authors.initials: J
authors.lastname: Liu