  In this work, we first review the issues on the singularities and the
boundary conditions in light cone gauge and how to regularize them properly.
Then we will further review how these singularities and the boundary conditions
can result in the gauge link at the infinity in the light cone direction in the
Drell-Yan process. Except for reviewing, we also have verified that the gauge
link at the light cone infinity has no dependence on the path not only for the
Abelian field but also for non-Abelian gauge field.
