**DIPS 2/2007**[tex source, PostScript, PDF file, dvi]-
**Title:**Iterated Differential Forms VI: Differential Equations.**Authors:**A. M. Vinogradov and L. VitaglianoWe describe the first term of the Λ

_{k-1}*C*-spectral sequence (see DIPS 5/06, or math.DG/0610917) of the diffiety (*E*,*C*),*E*being the infinite prolongation of an*l*-normal system of partial differential equations, and*C*the Cartan distribution on it.

See also arXiv: math.DG/0703761.

7 pages, LaTeX-2e.

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