  Starting from the two-particle Bethe-Salpeter equation in the ladder
approximation and integrating over the time component of momentum, we rederive
three dimensional scattering integral equations satisfying constraints of
relativistic unitarity and covariance, first derived by Weinberg and by
Blankenbecler and Sugar. These two-particle equations are shown to be related
by a transformation of variables. Hence we show how to perform and relate
identical dynamical calculation using these two equations. Similarly, starting
from the Bethe-Salpeter-Faddeev equation for the three-particle system and
integrating over the time component of momentum, we derive several three
dimensional three-particle scattering equations satisfying constraints of
relativistic unitarity and covariance. We relate two of these three-particle
equations by a transformation of variables as in the two-particle case. The
three-particle equations we derive are very practical and suitable for
performing relativistic scattering calculations.
