**DIPS 5/2006**[tex source, PostScript, PDF file, dvi]-
**Title:**Iterated Differential Forms IV:*C*-Spectral Sequence.**Authors:**A. M. Vinogradov and L. VitaglianoFor the multiple differential algebra of iterated differential forms on a diffiety

*(O,C)*an analogue of*C*-spectral sequence is constructed. The first term of it is naturally interpreted as the algebra of*secondary*iterated differential forms on*(O,C)*. This allows to develop*secondary tensor analysis*on generic diffieties, some simplest elements of which are sketched here. The presented here general theory will be specified to infinite jet spaces and infinitely prolonged PDEs in subsequent notes.

To appear in Doklady Akademii Nauk (Doklady Mathematics). See also arXiv: math.DG/0610917.

7 pages, LaTeX-2e.

To compile source files (**.tex**) one needs the title page style files titlatex.tex.