A formalism for a complete partial-wave expansion of the four-nucleon Green's function is given by generalizing a standard method. All of the constraints imposed by the symmetry properties (parity, time reversal, and exchange symmetry) are worked out, and an extended unitarity condition is shown to be satisfied. The use of Pad6 approximations to the Green's function is shown to provide a physical amplitude which is unitary, has correct threshold behavior in all waves, and has good analyticity properties. Therefore, such a scheme is well suited to explore beyond the Born term the dynamical content of various Lagrangian models proposed for the nucleon-nucleon interaction.
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