**DIPS 05/2002**[tex source, PostScript, PDF file, dvi]-
**Title:**Scalar second order evolution equations possessing an irreducible sl_{2}-valued zero curvature representation.**Author:**Michal MarvanWe find all scalar second order evolution equations possessing an sl

_{2}-valued zero curvature representation that is not reducible to a proper subalgebra of sl_{2}. None of these zero-curvature representations admits a parameter.

10 pages, LaTeX-2e.

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