no. 1

A rotation invariant differential equation for vector fields
Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 9 (1982) no. 1, pp. 159-174. 
@article{ASNSP_1982_4_9_1_159_0,
     author = {Reimann, H. M.},
     title = {A rotation invariant differential equation for vector fields},
     journal = {Annali della Scuola Normale Superiore di Pisa - Classe di Scienze},
     pages = {159--174},
     publisher = {Scuola normale superiore},
     volume = {Ser. 4, 9},
     number = {1},
     year = {1982},
     zbl = {0491.35027},
     mrnumber = {664106},
     language = {en},
     url = {http://www.numdam.org/item/ASNSP_1982_4_9_1_159_0/}
}
Reimann, H. M. A rotation invariant differential equation for vector fields. Annali della Scuola Normale Superiore di Pisa - Classe di Scienze, Série 4, Tome 9 (1982) no. 1, pp. 159-174. http://www.numdam.org/item/ASNSP_1982_4_9_1_159_0/

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