  Sea-Displacement Operators for fermions are defined in terms of the Fermi
fields in a one-component Fermi system. The main conclusions of this article
fully corroborate the conjectures made in our earlier works and provide a
mathematically rigorous foundations for these works. These ideas are
generalised to electron-hole systems where we are able to explore clearly the
nature of exciton-exciton interactions. We find that exciton-exciton
interactions in an ideal model of GaAs are not adequately treated as simply of
the two-body type; rather, the interactions are mediated by the exchange of
other bosons that are present in the system. These bosons are identified
explicitly and the exciton Green function is calculated. This excercise is also
intended to be a precursor to a systematic nonperturbative treatment of gauge
theories.
