By using an invariant related to free Lie algebras, we give a criterion of non existence of isomorphism for the Pfaffian systems.
@article{urn:eudml:doc:44392, title = {Alg\`ebres de Lie libres associ\'ees a un syst\`eme de Pfaff.}, journal = {Revista Matem\'atica de la Universidad Complutense de Madrid}, volume = {13}, year = {2000}, pages = {183-192}, zbl = {1017.58002}, mrnumber = {MR1794909}, language = {fr}, url = {http://dml.mathdoc.fr/item/urn:eudml:doc:44392} }
Ouazzani, Amina. Algèbres de Lie libres associées a un système de Pfaff.. Revista Matemática de la Universidad Complutense de Madrid, Tome 13 (2000) pp. 183-192. http://gdmltest.u-ga.fr/item/urn:eudml:doc:44392/