A continuous, constructive solution to Hilbert's 17th problem.
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C.N. Delzell (1984)
Inventiones mathematicae
Paweł Gładki (2016)
Communications in Mathematics
In this note we provide a direct and simple proof of a result previously obtained by Astier stating that the class of spaces of orderings for which the pp conjecture holds true is closed under sheaves over Boolean spaces.
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