  We study the half advanced and half retarded Wheeler Green function and its
relation to Feynman propagators. First for massless equation. Then, for
Klein-Gordon equations with arbitrary mass parameters; real, imaginary or
complex. In all cases the Wheeler propagator lacks an on-shell free
propagation. The Wheeler function has support inside the light-cone (whatever
the mass). The associated vacuum is symmetric with respect to annihilation and
creation operators.
  We show with some examples that perturbative unitarity holds, whatever the
mass (real or complex). Some possible applications are discussed.
