1. [A] Arosio, A.: Global (in time) solution of the approximated non-linear string equation of G.F. Carrier and R. Narashima. Comment. Math. Univ. Carol.26, 169–171 (1985)
2. [AS1] Arosio, A., Spagnolo, S.: Global existence for abstract evolution equations of weakly hyperbolic type. J. Math. Pures Appl.65, 263–305 (1986)
3. Collège de France seminar;A. Arosio,1984
4. [B] Bernstein, S.: Sur une classe d'équations fonctionnelles aux dérivées partielles. Izv. Akad. Nauk SSSR, Sér. Mat.4, 17–26 (1940)
5. [D] Dickey, R.W.: Infinite systems of nonlinear oscillation equations, related to the string. Proc. Am. Math. Soc.23, 459–468 (1969); Infinite systems of nonlinear oscillation equations. J. Differ. Equations8, 16–26 (1970)