1. L. Amerio and G. Prouse. — “Study of the motion of a string vibrating against an obstacle”, Rend, di Mat., Ser. 6, 8, n° 2, 1975, P· 563–585.
2. L. Amerio. — “Su un problema di vincoli unilaterali per l’equazione non omogenea delia corda vibrante”, Pubbl. I.A.C., Ser. III, 109, 1976, p. 1–11.
3. L. Amerio. — “On the motion of a string vibrating through a moving ring with a Continuously variable diameter”, Atti Accad. Naz. Lincei Rend. Cl. Sci. Fis. Natur, Ser. VIII, 62, n° 2, 1977, P. 134–142.
4. L. Amerio. — “Continuous solutions of the problem of a string vibrating against an obstacle”, Rend. Sem. Mat. Univ. Padova, 52, 1978, p. 67–96.
5. L. Amerio. — “A unilateral problem for a nonlinear vibrating string equation”, Atti Accad. Naz. Lincei Rend. Cl. Sci. Fis. Natur., Ser. VIII, 64, n° 1, 1978, p. 8–21.