On positive definite functions and some related functions on hypergroups (Q2910515)

The authors establish the notion of completely monotone and conditionally exponentially convex functions on commutative hypergroups. The latter notion seems to be connected with the well-known of negative definite functions.NEWLINENEWLINEThe authors claim to prove some statements for these classes of functions. As some notions are not explained like the space \(\hat X_+\), the meaning of several results remains unclear. Moreover, in Section 3, the authors systematically write \(f(x+y)\) for functions \(f\) on a hypergroup, which is not correct.