no. 1
Asymptotics for □u=m 2 u+G(x,t,u,u x ,u t ), I. Global existence and decay
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 3, Tome 26 (1972) no. 1, pp. 33-65. 
@article{ASNSP_1972_3_26_1_33_0,
     author = {Chadam, John M.},
     title = {Asymptotics for $\square \, u = m^2 u + G (x, t, u, u\_x, u\_t),$ I. Global existence and decay},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {33--65},
     publisher = {Scuola normale superiore},
     volume = {Ser. 3, 26},
     number = {1},
     year = {1972},
     language = {en},
     url = {archive.numdam.org/item/ASNSP_1972_3_26_1_33_0/}
}
Chadam, John M. Asymptotics for $\square \, u = m^2 u + G (x, t, u, u_x, u_t),$ I. Global existence and decay. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 3, Tome 26 (1972) no. 1, pp. 33-65. http://archive.numdam.org/item/ASNSP_1972_3_26_1_33_0/

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