On a Gibbs characterization of normalized generalized Gamma processes

We show that a Gibbs characterization of normalized generalized Gamma processes, recently obtained in Lijoi, Pr"unster and Walker (2007), can alternatively be derived by exploiting a characterization of exponentially tilted Poisson-Kingman models stated in Pitman (2003). We also provide a completion of this result investigating the existence of normalized random measures inducing exchangeable Gibbs partitions of type $\alpha \in (-\infty, 0]$.