Not a prescription but an identity: Mandelstam-Leibbrandt
  After some considerations and coincidences that appear when working in the light-cone gauge, in both the Mandelstam-Leibbrandt prescription and the covariantization method, we suspect that there must be some connection between them. This work shows that we were right and it is practically trivial to demonstrate that relationship. And since the covariantization method is not a prescription, this implies that the results of Mandelstam and Leibbrandt are not prescriptions too, but they are a identities from light-cone gauge coordinates. 
Ricardo Bentin