@article{CM_1981__44_1-3_241_0,
     author = {Nacinovich, Mauro},
     title = {On the absence of {Poincar\'e} lemma for some systems of partial differential equations},
     journal = {Compositio Mathematica},
     pages = {241--303},
     publisher = {Sijthoff et Noordhoff International Publishers},
     volume = {44},
     number = {1-3},
     year = {1981},
     mrnumber = {662464},
     zbl = {0487.58026},
     language = {en},
     url = {http://www.numdam.org/item/CM_1981__44_1-3_241_0/}
}