In this paper we consider the following question: Let S be a semialgebraic subset of a real algebraic set V, and let φ: S → Z be a function on S. Is φ the restriction of an algebraically constructible function on V, i.e. a sum of signs of polynomials on V? We give an effective method to answer this question when φ(S) ⊂ {-1,1} or dim S ≤ 2 or S is basic.
We present a characterization of sums of signs of global analytic functions on a real analytic manifold M of dimension two. Unlike the algebraic case, obstructions at infinity are not relevant: a function is a sum of signs on M if and only if this is true on each compact subset of M. This characterization gives a necessary and sufficient condition for an analytically constructible function, i.e. a linear combination with integer coefficients of Euler characteristic of fibers of proper analytic morphisms,...
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