  In a series of recent papers it was shown that, when the attractive s-wave
interaction is dominant, the spin-orbit coupled fermions form a bound state.
Attributed to a convenient momentum representation, it became a common
condition of agreement to express the bound state as a function of the
center-of-mass momentum Q. In this letter we prove that the bound state of
Rashba fermions does not depend on the chosen representation. That is, all the
states characterized by nonzero Q fail to obey the translation symmetry.
