@article{RSMUP_1977__57__167_0,
     author = {Bratti, Giuliano},
     title = {A density theorem about some system},
     journal = {Rendiconti del Seminario Matematico della Universit\`a di Padova},
     pages = {167--172},
     publisher = {Seminario Matematico of the University of Padua},
     volume = {57},
     year = {1977},
     mrnumber = {526189},
     zbl = {0415.35016},
     language = {en},
     url = {http://archive.numdam.org/item/RSMUP_1977__57__167_0/}
}