@article{10_1090_S0894_0347_97_00231_2,
     author = {Chanillo, Sagun and Treves, Fran\c{c}ois},
     title = {Local exactness in a class of differential complexes},
     journal = {Journal of the American Mathematical Society},
     pages = {393--426},
     year = {1997},
     volume = {10},
     number = {2},
     doi = {10.1090/S0894-0347-97-00231-2},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-97-00231-2/}
}