  We show how to attach an external photon to a system of three strongly
interacting nucleons described by three-body scattering equations. Our method
involves the idea of gauging the scattering equations themselves, and results
in electromagnetic amplitudes where the external photon is effectively coupled
to every part of every strong interaction diagram in the model. Current
conservation is therefore implemented in the theoretically correct fashion. In
this way we obtain the expressions needed to calculate all possible
electromagnetic processes of the three-nucleon system including the
electromagnetic form factors of the three-body bound state, pd -> pd gamma,
gamma He3 -> pd, gamma He3 -> ppn, etc. As the photon is coupled everywhere in
the strong interaction model, a unified description of the NNN-gamma NNN system
is obtained. An interesting aspect of our results is the natural appearance of
subtraction terms needed to avoid the overcounting of diagrams. We have also
applied the gauging of equations method to the four-dimensional description of
the piNN system which, because of the possibility of pion absorption, has
overcounting problems all of its own, and is therefore much more complicated
than the NNN case discussed here. Despite these complications, the gauging
procedure itself is very simple and leads easily to a unified description of
the piNN-gamma piNN system.
