no. 1
An example of irregular solution to a nonlinear Euler-Lagrange elliptic system with real analytic coefficients
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 23 (1996) no. 1, pp. 57-67 
@article{ASNSP_1996_4_23_1_57_0,
     author = {Hao, Wenge and Leonardi, Salvatore and Ne\v{c}as, Jind\v{r}ich},
     title = {An example of irregular solution to a nonlinear {Euler-Lagrange} elliptic system with real analytic coefficients},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {57--67},
     year = {1996},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 23},
     number = {1},
     mrnumber = {1401417},
     zbl = {0864.35031},
     language = {en},
     url = {https://www.numdam.org/item/ASNSP_1996_4_23_1_57_0/}
}
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Hao, Wenge; Leonardi, Salvatore; Nečas, Jindřich. An example of irregular solution to a nonlinear Euler-Lagrange elliptic system with real analytic coefficients. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 23 (1996) no. 1, pp. 57-67. https://www.numdam.org/item/ASNSP_1996_4_23_1_57_0/

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