“…Therefore it seems attractive to start investigations assuming that the metric graph and the vertex conditions are fixed. The simplest graph to be considered is the star graph formed by a finite number of compact edges, and the corresponding inverse problem resembles very much the inverse problem on a single interval, where the potential is determined by two spectra [14,30,[33][34][35]. The case of general trees has also been studied and we have a rather good understanding of the problem [2,8,9,31,37].…”