1. Melis, A. and Piras, B.: ?An extension of Szebehely's problem to holonomic systems?, Celest. Mech., 32 (1984), 87?92.
2. Melis, A. and Borghero, F.: ?On Szebehely's problem extended to holonomic systems with a given integral of motion?, Meccanica, J. Ital. Ass. of Theor. Appl. Mech. 21 (1986), 71?74.
3. Borghero, F.: ?On the determination of forces acting on a particle describing orbits on a given surface?, Rend. di Matem. di Roma, Serie VII, 6 (1986), 503?518.
4. Borghero, F.: ?Variational determination of the generalized Szebehely's equations?, Rend. Sem. Mat. Unine Politec. Torino, 45 (1987), 125?135.
5. Melis, A. and Piras, B.: ?On a generalization of Szebehely's problem?, Rend. Sem. Fac. Se. Univ. Cagliari, L11 (1982), 73?78.