  For relativistic three-body calculations, essentially two different
approaches are in use: field theory and relativistic direct interactions.
Results for relativistic corrections of the triton binding energy obtained from
the two approaches differ even in their sign, which is rather puzzling. In this
paper, we discuss the origin of such discrepancy. We show that the use of an
invariant two-body amplitude, as done in the field-theoretic approach,
increases the triton binding energy by about 0.30 MeV. This may explain a large
part of the discrepancy.
