up to one, when one considers all contributions from these chains. The ordering, in both $p_+$ and $p_-$, and the absence of the non-eikonal form factors, implies that LDC is forward-backward symmetric. If one starts from the probe end, which has large $q_{-}$, and follows the chain towards the proton end, which has large $P_+$, the situation will look the same, the minus and plus components will just change roles and we will have exactly the same ordering and the same distribution function. In the LDC model the distribution function satisfies the following evolution equation (see eq.43 in [@e1]) $$\frac{\partial \mathcal{F}(x,k_{\perp}^2)}{\partial \log (1/x)} \approx \bar{\alpha}
\biggl[\int^{k_{\perp}^2}
  \frac{dk_{\perp}^{'2}}{k_{\perp}^{'2}}\mathcal{F}(x,k_{\perp}^{'2}) + \int_{k_{\perp}^2}
  \frac{dk_{\perp}^{'2}}{k_{\perp}^{'2}} \frac{k_{\perp}^{2}}{k_{\perp}^{'2}}
  \mathcal{F}(x\frac{k_{\perp}^{'2}}{k_{\perp}^{2}}, k_{\perp}^{'2}) \biggr]$$ Here $k_{\perp}^{2}$ is the transverse momentum of the last gluon in the chain while $k_{\perp}^{'2}$ is the momentum in the step before. The first term here is the DGLAP contribution where the transverse momentum increases in the last step, while the second term contains the probability that the transverse momentum decreases in the last step. For a more detailed discussion on these models, see [@e11].

Mueller’s Dipole Formulation
----------------------------

The idea of dipoles as emitters of radiation is quite natural in QCD. Consider the two diagrams 