  In a series of recent publications, a new approach to the non-relativistic
reduction of the electromagnetic current operator in calculations of
electro-nuclear reactions has been introduced. In one of these papers, the
conjecture that at energies of a few GeV, the bulk of the relativistic effects
comes from the current and not from the nuclear dynamics was made, based on the
large relativistic effects in the transverse-longitudinal response. Here, we
explicitly compare a fully relativistic, manifestly covariant calculation
performed with the Gross equation, with a calculation that uses a
non-relativistic wave function and a fully relativistic current operator. We
find very good agreement up to missing momenta of 400 MeV/c, thus confirming
the previous conjecture. We discuss slight deviations in cross sections for
higher missing momenta and their possible origin, namely p-wave contributions
and off-shell effects.
