title: Comment on "Existence and design of trans-vacuum-speed metamaterials".
abstract: It is shown that metamaterials considered by Phys. Rev. E 68, 026612 (2003)]] as media that support trans-vacuum-speed pulses must exhibit instantaneous response. Thus, they are not physically realizable as linear passive materials.
authors.affiliation: Radio Laboratory, Helsinki University of Technology, P.O. Box 3000, FIN-02015 HUT, Finland. sergei.tretyakov@hut.fi
authors.forename: S A
authors.initials: SA
authors.lastname: Tretyakov