no. 2
Propagation of singularities for a first order semi-linear system in ℂ n+1
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 12 (1985) no. 2, pp. 173-189. 
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     author = {Kobayashi, Takao},
     title = {Propagation of singularities for a first order semi-linear system in $\mathbb {C}^{n+1}$},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {173--189},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 12},
     number = {2},
     year = {1985},
     mrnumber = {829051},
     zbl = {0594.35002},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1985_4_12_2_173_0/}
}
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Kobayashi, Takao. Propagation of singularities for a first order semi-linear system in $\mathbb {C}^{n+1}$. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 12 (1985) no. 2, pp. 173-189. http://www.numdam.org/item/ASNSP_1985_4_12_2_173_0/

[1] J. Rauch - M. Reed, Jump discontinuities of semi-linear strictly hyperbolic systems in two variables: creation and propagation, Comm. Math. Phys., 81 (1981), pp. 203-227. | MR | Zbl

[2] J. Rauch - M. Reed, Nonlinear microlocal analysis of semilinear hyperbolic systems in one space dimension, Duke Math. J., 49 (1982), pp. 397-475. | MR | Zbl

[3] T. Ishii, Construction of solutions with singularities for semi-linear equations, in preparation.