Haeri [@H91], takes the form $$\begin{aligned}
\Gamma_\mu^{\rm H}(p,q) & = & \frac{p^2 A(p^2) - q^2 A(q^2)}{p^2 - q^2} 
                \gamma_\mu +  \frac{A(p^2) - A(q^2)}{p^2 - q^2} 
           \gamma\cdot p \gamma_\mu \gamma\cdot q \nonumber \\
 & & -i \frac{B(p^2) - B(q^2)}{p^2 - q^2} 
     \left(\gamma\cdot p \gamma_\mu +  \gamma_\mu \gamma\cdot q\right).  
                         \label{Hver}\end{aligned}$$ It satisfies the above criteria and therefore must be of the form Eq. (\[genver\]). Munczek [@Mpr] has shown that the Haeri vertex is identical to the spectral representation of the vertex used in the gauge technique, and this has in turn been employed in ref. [@DL97].

Gluon propagator
----------------

In a general covariant gauge, the gluon propagator takes the form $$g^2 D_{\mu \nu}(k) = 
  \left(\delta_{\mu \nu} - \frac{k_\mu k_\nu}{k^2}\right) \Delta(k^2) 
        + g^2 \xi \frac{k_\mu k_\nu}{k^4},    \label{gprop}$$ where $\xi$ is the gauge fixing parameter. Perhaps the simplest Ansatz which has proved useful for modelling QCD is the ‘infrared dominant’ model [@M86; @BRW92] $$\Delta_{\rm IR}(k^2) = \frac{3}{16}(2\pi)^4 \mu^2 \delta^4(k).  \label{delpr}$$ In applications to hadronic physics, $\mu$ is usually taken to be of the order of 1 GeV [@MN83], which is the typical scale of QCD. An obvious disadvantage of this model is that it neglects completely any intermediate or ultraviolet behaviour. One can go 