  We present detailed analyses of the 3-body interactions of D-particles from
both sides of 11 dimensional supergravity and Matrix theory. In supergravity,
we derive a complete expression for the classical bosonic effective action for
D-particles including 2-and 3-body interaction terms. In Matrix theory, we
compute 1-particle irreducible contributions to the eikonal phase shift in the
two-loop approximation. The results precisely agree with the predictions from
supergravity and thus provide a strong support to the discrete light-cone
interpretation of the Matrix-theory conjecture as a possible nonperturbative
definition of M-theory.
