@article{ASNSP_2000_4_29_2_253_0,
     author = {Landes, R\"udiger},
     title = {On the angle condition for the perturbation of elliptic systems},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {253--268},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 29},
     number = {2},
     year = {2000},
     mrnumber = {1784175},
     zbl = {0961.35042},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_2000_4_29_2_253_0/}
}