On the stability of the Dirichlet problem for the vibrating string equation
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Serie 4, Volume 6 (1979) no. 4, p. 719-728 
@article{ASNSP_1979_4_6_4_719_0,
     author = {Papi Frosali, Gloria},
     title = {On the stability of the Dirichlet problem for the vibrating string equation},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 6},
     number = {4},
     year = {1979},
     pages = {719-728},
     zbl = {0429.35043},
     mrnumber = {563341},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1979_4_6_4_719_0}
}

Papi Frosali, Gloria. On the stability of the Dirichlet problem for the vibrating string equation. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Serie 4, Volume 6 (1979) no. 4, pp. 719-728. http://www.numdam.org/item/ASNSP_1979_4_6_4_719_0/

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