Real Algebraic and Analytic Geometry |

Sums of squares in real rings.

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Submission: 2002, October 25.

*Abstract:
Let $A$ be an excellent ring. We show that if the real dimension of $A$
is $\geq 3$ then $A$ has
infinite Pythagoras number and there exist positive semidefinite
elements in $A$ which are not sum of squares on $A$.*

**Full text**:
pdf=http://www.mat.ucm.es/~jesusr/pdfs/dim3.pdf

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