  Recently, Eremin and Manske [1] presented a oneband Fermi-liquid theory for
the in-plane magnetic anisotropy in untwinned high-Tc superconductor
YBa2Cu3O6:85 (YBCO). They claimed that they found good agreement with inelastic
neutron scattering (INS) spectra. In this Comment, we point out that their
conclusion on this important problem may be questionable due to an error in
logic about the orthorhombicity delta_0 characterizing the lattice structure of
YBCO. In Ref. [1], a single band at delta_0>0 is proved to be in accordance
with the angle resolved photoemission spectroscopy (ARPES) on untwinned YBCO.
But in their Erratum in PRL[3], they admit that delta_0= -0.03 was used to fit
the INS data. Hence publications [1,3] contain errors that we believe
invalidate their approach.
