  In this paper, we study some properties of multi-solitons for the non-linear
Schr{\"o}dinger equations in R^d with general non-linearities. Multi-solitons
have already been constructed in H^1, successively by Merle, by Martel and
Merle, and by C{\^o}te, Martel and Merle. We show here that multi-solitons are
smooth, depending on the regularity of the non-linearity. We obtain also a
result of uniqueness in some class, either when the ground states are all
stable, or in the mass-critical case.
