@article{JEDP_1976____A4_0,
     author = {Bolley, Pierre and Camus, Jacques},
     title = {R\'egularit\'e pour des syst\`emes \`a coefficients constants},
     journal = {Journ\'ees \'equations aux d\'eriv\'ees partielles},
     eid = {4},
     pages = {1--19},
     publisher = {Ecole polytechnique},
     year = {1976},
     language = {fr},
     url = {http://archive.numdam.org/item/JEDP_1976____A4_0/}
}