  The completeness, together with the orthonormality, of the eigenfunctions of
the Dirac Hamiltonian with a step potential is shown explicitly. These
eigenfunctions describe the scattering process of a relativistic fermion off
the step potential and the resolution of the identity in terms of them
(completeness) is shown by explicitly summing them up, where appropriate
treatments of the momentum integrations are crucial. The result would bring
about a basis on which a field theoretical treatment for such a system can be
developed.
