“…The problem of description of superintegrable systems (i.e., systems with closed trajectories in a certain domain) in the class of rotationally symmetric natural mechanical systems goes back to Bertrand and Darboux. Natural mechanical systems of Bertrand's type were described under several restrictions by Bertrand [1], Darboux [2], Besse [3], Perlick [4], Zagryadskii, Kudryavtseva and Fedoseev [5], Kudryavtseva and Fedoseev [6,7,8] and others (cf. a survey in [5]).…”