“…Furthermore, while in the case of the ordinary spacelike Cauchy problem in general relativity the constraints are standard, depend only of the geometric nature of the Einstein's equations (i.e. the so called Hamiltonian and momentum constraints) [3], [5], in the case of the characteristic initial value problem, one faces the difficult task of highlighting additional gauge-dependent constraints essential to the construction of the full set of initial data [6], [9], [10], [12], [17], [18], [19], [20], [21], [22]. These latter are induced by: the evolution system deduced of the splitting of the Einstein equations by the choice of a gauge, the form of the stress-energy momentum tensor of the matter involved, and their hierarchy depends heavily on the prescribed free data.…”