1. The energy theorem in the impact of a string vibrating against a pointshaped obstacle;Citrini;Atti della Accademia Nazionale dei Lincei Rendiconti,1977
2. Continuous solutions of the problem of a string vibrating against an obstacle;Amerio;Rendiconti del Seminario Mathematico della Universita di Padova,1978
3. A hyperbolic problem of second order with unilateral constraints: the vibrating string with a concave obstacle;Schatzman;Journal of Mathematical Analysis and Applications,1980
4. Almost periodic motion of a string vibrating against a straight fixed obstacle;Haraux;Nonlinear Analysis, Theory, Methods and Applications,1983
5. The sitar string, a vibrating string with a one-sided inelastic constraint;Burridge;SIAM Journal of Applied Mathematics,1982