Comment on "Acoustics of tachyon Fermi gas" [E. Trojan and G.V. Vlasov,
  arXiv:1103.2276 (hep-ph)]
  In contrast to Trojan and Vlasov [arXiv:1103.2276 (hep-ph)], it is found that
an ideal Fermi gas of tachyons has a subluminous velocity of sound for any
particle density and, therefore, the causality condition for a tachyon gas
holds always true. Also, an ideal Fermi gas of tachyons never possesses an
exotic equation of state with the pressure exceeding the energy density.
